Picture coding method, picture coding apparatus, picture decoding method, and picture decoding apparatus

ABSTRACT

A picture coding method includes: performing a first derivation process for deriving a first merging candidate which includes a candidate set of a prediction direction, a motion vector, and a reference picture index for use in coding of a current block; performing a second derivation process for deriving a second merging candidate; selecting a merging candidate to be used in the coding of the current block from among the first and second merging candidates; and attaching an index for identifying the selected merging candidate to the bitstream; wherein the first derivation process is performed so that a total number of the first merging candidates does not exceed a predetermined number, and the second derivation process is performed when the total number of the first merging candidates is less than a predetermined maximum number of merging candidates.

FIELD

One or more exemplary embodiments disclosed herein relate to a picturecoding method and a picture decoding method.

BACKGROUND

Generally, in coding processing of a moving picture, the amount ofinformation is reduced by compression for which temporal redundancy andspatial redundancy in a moving picture is utilized. Generally, transforminto frequency domain is performed as a method in which spatialredundancy is utilized, and coding using prediction between pictures(the prediction is hereinafter referred to as inter prediction) isperformed as a method of compression for which temporal redundancy isutilized. In the inter prediction coding, a current picture is codedusing, as a reference picture, a coded picture which precedes or followsthe current picture in order of display time. A motion vector is derivedby estimating motion between the current picture and the referencepicture. Then, difference between picture data of the current pictureand prediction picture data obtained by motion compensation based on thederived motion vector is calculated to reduce temporal redundancy (seeNon-patent Literature 1, for example). In the motion estimation,difference values between current blocks in the current picture andblocks in the reference picture are calculated, and a block having thesmallest difference value in the reference picture is determined as areference block. Then, a motion vector is estimated for the currentblock and the reference block.

CITATION LIST Non Patent Literature

-   [Non-patent Literature 1] ITU-T Recommendation H.264 “Advanced video    coding for generic audiovisual services”, March 2010-   [Non-patent Literature 2] JCT-VC, “WD3: Working Draft 3 of    High-Efficiency Video Coding”, JCTVC-E603, March 2011

SUMMARY Technical Problem

It is still desirable to increase coding efficiency in coding anddecoding of pictures using inter prediction with the above-describedconventional technique.

Non-limiting and exemplary embodiments provide picture coding methodsand picture decoding methods with which coding efficiency in coding anddecoding of pictures using inter prediction is increased.

Solution to Problem

In one general aspect, the techniques disclosed here feature a picturecoding method which is a method for coding a picture on a block-by-blockbasis to generate a bitstream and includes: performing a firstderivation process for deriving a first merging candidate which includesa candidate set of a prediction direction, a motion vector, and areference picture index for use in coding of a current block; performinga second derivation process for deriving a second merging candidatewhich includes a candidate set of a prediction direction, a motionvector, and a reference picture index for use in the coding of thecurrent block, the second derivation process being different from thefirst derivation process; selecting a merging candidate to be used inthe coding of the current block from among the first merging candidateand the second merging candidate; and attaching an index for identifyingthe selected merging candidate to the bitstream, wherein in theperforming of a first derivation process, the first derivation processis performed so that a total number of the first merging candidates doesnot exceed a predetermined number, and the second derivation process isperformed when the total number of the first merging candidates is lessthan a predetermined maximum number of merging candidates.

These general and specific aspects can be implemented as a system, amethod, an integrated circuit, a computer program, a computer-readablerecording medium such as a CD-ROM (compact disc read-only memory), or asany combination of a system, a method, an integrated circuit, a computerprogram, and a computer-readable recording medium.

Additional benefits and advantages of the disclosed embodiments will beapparent from the Specification and Drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the Specification and Drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

Advantageous Effects

A picture coding method according to one or more exemplary embodimentsor features disclosed herein provide increased coding efficiency incoding and decoding of pictures using inter prediction.

BRIEF DESCRIPTION OF DRAWINGS

These and other advantages and features will become apparent from thefollowing description thereof taken in conjunction with the accompanyingDrawings, by way of non-limiting examples of embodiments disclosedherein.

FIG. 1A is a diagram for illustrating an exemplary reference picturelist for a B-picture.

FIG. 1B shows an example of a reference picture list 0 (L0) for aprediction direction 0 in bi-prediction of a B-picture.

FIG. 1C shows an example of a reference picture list 1 (L1) for aprediction direction 1 in bi-prediction of a B-picture.

FIG. 2 is a diagram for illustrating motion vectors for use in atemporal motion vector prediction mode.

FIG. 3 shows an exemplary motion vector of a neighboring block used inthe merging mode.

FIG. 4 is a diagram for illustrating an example of a merging candidatelist.

FIG. 5 shows a relationship between the size of a merging candidate listand bit sequences assigned to merging candidate indices.

FIG. 6 is a flowchart showing an example of a process for coding of acurrent block when the merging mode is used.

FIG. 7 is a flowchart showing a process for decoding using the mergingmode.

FIG. 8 shows syntax for attachment of merging candidate indices to abitstream.

FIG. 9 is a block diagram showing a configuration of a picture codingapparatus according to Embodiment 1.

FIG. 10A is a flowchart showing processing operations of a picturecoding apparatus according to Embodiment 1.

FIG. 10B is a flowchart showing derivation of merging candidatesaccording to Embodiment 1.

FIG. 11 shows an example of a merging candidate list generated by thepicture coding apparatus according to Embodiment 1.

FIG. 12 is a block diagram showing a configuration of a picture decodingapparatus according to Embodiment 2.

FIG. 13A is a flowchart showing processing operations of the picturedecoding apparatus according to Embodiment 2.

FIG. 13B is a flowchart showing derivation of merging candidatesaccording to Embodiment 2.

FIG. 14 is a block diagram showing a configuration of a picture codingapparatus according to Embodiment 3.

FIG. 15 is a flowchart showing processing operations of the picturecoding apparatus according to Embodiment 3.

FIG. 16 is a flowchart showing the process for selecting a mergingcandidate according to Embodiment 3.

FIG. 17 is a block diagram showing a configuration of a picture decodingapparatus according to Embodiment 4.

FIG. 18 is a flowchart showing processing operations of the picturedecoding apparatus according to Embodiment 4.

FIG. 19 is a flowchart showing derivation of a zero merging candidateaccording to Embodiment 5.

FIG. 20 shows an example of a derived zero merging candidate inEmbodiment 5.

FIG. 21 is a flowchart showing derivation of a combined mergingcandidate according to Embodiment 6.

FIG. 22 is a flowchart showing derivation of a scaling merging candidateaccording to Embodiment 7.

FIG. 23 shows an example of a motion vector and a reference pictureindex calculated in Embodiment 7.

FIG. 24 shows an overall configuration of a content providing system forimplementing content distribution services.

FIG. 25 shows an overall configuration of a digital broadcasting system.

FIG. 26 shows a block diagram illustrating an example of a configurationof a television.

FIG. 27 shows a block diagram illustrating an example of a configurationof an information reproducing/recording unit that reads and writesinformation from and on a recording medium that is an optical disk.

FIG. 28 shows an example of a configuration of a recording medium thatis an optical disk.

FIG. 29A shows an example of a cellular phone.

FIG. 29B is a block diagram showing an example of a configuration of acellular phone.

FIG. 30 illustrates a structure of multiplexed data.

FIG. 31 schematically shows how each stream is multiplexed inmultiplexed data.

FIG. 32 shows how a video stream is stored in a stream of PES packets inmore detail.

FIG. 33 shows a structure of TS packets and source packets in themultiplexed data.

FIG. 34 shows a data structure of a PMT.

FIG. 35 shows an internal structure of multiplexed data information.

FIG. 36 shows an internal structure of stream attribute information.

FIG. 37 shows steps for identifying video data.

FIG. 38 shows an example of a configuration of an integrated circuit forimplementing the moving picture coding method and the moving picturedecoding method according to each of embodiments.

FIG. 39 shows a configuration for switching between driving frequencies.

FIG. 40 shows steps for identifying video data and switching betweendriving frequencies.

FIG. 41 shows an example of a look-up table in which video datastandards are associated with driving frequencies.

FIG. 42A is a diagram showing an example of a configuration for sharinga module of a signal processing unit.

FIG. 42B is a diagram showing another example of a configuration forsharing a module of the signal processing unit.

DESCRIPTION OF EMBODIMENTS Underlying Knowledge Forming Basis of thePresent Disclosure

In a moving picture coding scheme already standardized, which isreferred to as H.264, the amount of information is reduced bycompression using three types of pictures: I-picture, P-picture, andB-picture.

The I picture is not coded using inter prediction. Specifically, theI-picture is coded by prediction within the picture (the prediction ishereinafter referred to as intra prediction). The P-picture is codedusing inter prediction with reference to one previously coded picturepreceding or following the current picture in order of display time. TheB-picture is coded using inter prediction with reference to twopreviously coded pictures preceding and following the current picture inorder of display time.

In coding using inter prediction, a reference picture list foridentifying a reference picture is generated. In the reference picturelist, reference picture indices are assigned to coded reference picturesto be referenced in inter prediction. For example, two reference picturelists (L0 and L1) are generated for a B-picture because it is coded withreference to two pictures.

FIG. 1A is a diagram for illustrating an exemplary reference picturelist for a B-picture. FIG. 1B shows an example of a reference picturelist 0 (L0) for a prediction direction 0 in bi-prediction. In thereference picture list 0, the reference picture index 0 having a valueof 0 is assigned to a reference picture 0 with a display order of 2. Thereference picture index 0 having a value of 1 is assigned to a referencepicture 1 with a display order of 1. The reference picture index 0having a value of 2 is assigned to a reference picture 2 with a displayorder of 0. In other words, a reference picture temporally closer to thecurrent picture in display order is assigned with a reference pictureindex having a smaller value.

FIG. 1C shows an example of a reference picture list 1 (L1) for aprediction direction 1 in bi-prediction. In the reference picture list1, the reference picture index 1 having a value of 0 is assigned to areference picture 1 with a display order of 1. The reference pictureindex 1 having a value of 1 is assigned to a reference picture 0 with adisplay order of 2. The reference picture index 1 having a value of 2 isassigned to a reference picture 2 with a display order of 0.

In this manner, reference picture indices assigned to a referencepicture may have values different between prediction directions (thereference pictures 0 and 1 in FIG. 1A), and may have the same value forboth directions (the reference picture 2 in FIG. 1A).

In a moving picture coding method referred to as H.264 (see Non-patentLiterature 1), a motion vector estimation mode is available as a codingmode for inter prediction of each current block in a B-picture. In themotion vector estimation mode, a difference value between picture dataof a current block and prediction picture data and a motion vector usedfor generating the prediction picture data are coded. In addition, inthe motion vector estimation mode, bi-prediction and uni-prediction canbe selectively performed. In bi-prediction, a prediction picture isgenerated with reference to two coded pictures one of which precedes acurrent picture to be coded and the other of which follows the currentpicture. In uni-prediction, a prediction picture is generated withreference to one coded picture preceding or following a current pictureto be coded.

Furthermore, in the moving picture coding method referred to as H.264, acoding mode referred to as a temporal motion vector prediction mode canbe selected for derivation of a motion vector in coding of a B-picture.The inter prediction coding method performed in temporal motion vectorprediction mode will be described below using FIG. 2 .

FIG. 2 is a diagram for illustrating motion vectors for use in thetemporal motion vector prediction mode. Specifically, FIG. 2 shows acase where a block a in a picture B2 is coded in temporal motion vectorprediction mode.

In the coding, a motion vector vb is used which has been used for codingof a block b in a picture P3, which is a reference picture following thepicture B2. The position of the motion vector vb in the picture P3 isthe same as the position of the block a in the picture B2 (the block bis hereinafter referred to as a “co-located block” of the block a). Themotion vector vb has been used for coding the block b with reference tothe picture P1.

Motion vectors parallel to the motion vector vb are used for obtainingtwo reference blocks for the block a from a preceding reference pictureand a following reference picture, that is, a picture P1 and a pictureP3. Then, the block a is coded using bi-prediction based on the twoobtained reference blocks. Specifically, the block a is coded withreference the picture P1 using a motion vector va1 and with reference tothe picture P3 using a motion vector vat.

In addition, a merging mode has been discussed which is an interprediction mode for coding of each current block in a B-picture or aP-picture (see Non-patent Literature 2). In the merging mode, a currentblock is coded using a set of a prediction direction, a motion vector,and a reference picture index which is a copy of a set thereof used forcoding a neighboring block of the current block. In the coding of acurrent block, an index and others indicating the set of a predictiondirection, a motion vector, and a reference picture index which is usedas a set for the coding of the neighboring block is attached to abitstream. This makes it possible to select, in decoding of the currentblock, the set of a prediction direction, a motion vector, and areference picture index used as a set for the coding of the neighboringblock. A concrete example is given below with reference to FIG. 3 .

FIG. 3 shows an exemplary motion vector of a neighboring block used inthe merging mode. In FIG. 3 , a neighboring block A is a coded blocklocated on the immediate left of a current block. A neighboring block Bis a coded block located immediately above the current block. Aneighboring block C is a coded block located immediately above to theright of the current block. A neighboring block D is a coded blocklocated immediately below to the left of the current block.

The neighboring block A is a block coded using uni-prediction in theprediction direction 0. The neighboring block A has a motion vectorMvL0_A having the prediction direction 0, which is a motion vector to areference picture indicated by a reference picture index RefL0_A for theprediction direction 0. Here, MvL0 represents a motion vector whichreferences a reference picture specified in a reference picture list 0(L0). MvL1 represents a motion vector which references a referencepicture specified in a reference picture list 1 (L1).

The neighboring block B is a block coded using uni-prediction in theprediction direction 1. The neighboring block B has a motion vectorMvL1_B having the prediction direction 1, which is a motion vector to areference picture indicated by a reference picture index RefL1_B for theprediction direction 1.

The neighboring block C is a block coded using intra prediction.

The neighboring block D is a block coded using uni-prediction in theprediction direction 0. The neighboring block D has a motion vectorMvL0_D having the prediction direction 0, which is a motion vector to areference picture indicated by a reference picture index RefL0_D for theprediction direction 0.

In the case illustrated in FIG. 3 , for example, a set of a predictiondirection, a motion vector, and a reference picture index with which thecurrent block can be coded with the highest coding efficiency isselected as a set of a prediction direction, a motion vector, and areference picture index of the current block from among such sets of theneighboring blocks A to D and a set of a prediction direction, a motionvector, and a reference picture index which are calculated using aco-located block in temporal motion vector prediction mode. One or morecandidate sets of a prediction direction, a motion vector, and areference picture index compose a merging candidate. A merging candidateindex indicating the selected merging candidate is attached to abitstream.

For example, when the merging candidate of the neighboring block A isselected, the current block is coded using the reference picture indexRefL0_A and the motion vector MvL0_A having the prediction direction 0.Then, only a merging candidate index having a value of 0 is attached toa bitstream, indicating that the merging candidate of the neighboringblock A as shown in FIG. 4 is used for the coding of the current block.The amount of information on a prediction direction, a motion vector,and a reference picture index is thereby reduced.

Furthermore, in the merging mode, a candidate which cannot be used forcoding of a current block (hereinafter referred to as an“unusable-for-merging candidate”), and a candidate having a set of aprediction direction, a motion vector, and a reference picture indexidentical to a set of a prediction direction, a motion vector, and areference picture index of any other merging block (hereinafter referredto as an “identical candidate”) are removed from the merging candidatelist as shown in FIG. 4 .

The total number of merging candidates is thus reduced, and thereby theamount of codes assigned to merging candidate indices is saved. Examplesof the merging candidate which cannot be used for coding of a currentblock includes: (1) a merging candidate of a block coded using intraprediction, (2) a merging candidate of a block outside the sliceincluding the current block or outside the boundary of a pictureincluding the current block, and (3) a merging candidate of a block yetto be coded.

In the example shown in FIG. 4 , the neighboring block C is a blockcoded using intra prediction. The merging candidate of the neighboringblock C (indicated by the merging candidate index having a value of 3)is an unusable-for-merging candidate and therefore removed from themerging candidate list. In addition, the neighboring block D isidentical in prediction direction, motion vector, and reference pictureindex to the neighboring block A. The merging candidate of theneighboring block D (indicated by the merging candidate index having avalue of 4) is therefore removed from the merging candidate list. As aresult, the final total number of merging candidates is three, and thesize of the merging candidate list is set at three.

Merging candidate indices are coded by variable-length coding byassigning bit sequences according to the size of each merging candidatelist as shown in FIG. 5 . In the merging mode, bit sequences assigned tomerging candidate indices are thus changed depending on the size of eachmerging candidate list, and thereby the amount of code is reduced.

FIG. 6 is a flowchart showing an example of a process for coding of acurrent block when the merging mode is used. In Step S1001, sets eachincluding a prediction direction, a motion vector, and a referencepicture index of neighboring blocks and a co-located block are obtainedas merging candidates. In Step S1002, identical candidates andunusable-for-merging candidates are removed from the merging candidates.In Step S1003, the total number of the merging candidates after theremoving is set as the size of the merging candidate list. In StepS1004, a merging candidate index to be used for coding of the currentblock is determined. In Step S1005, the determined merging candidateindex is coded by variable-length coding in bit sequence according tothe size of the merging candidate list.

FIG. 7 is a flowchart showing an example of a process for decoding usingthe merging mode. In Step S2001, sets each including a predictiondirection, a motion vector, and a reference picture index of neighboringblocks and a co-located block are obtained as merging candidates. InStep S2002, identical candidates and unusable-for-merging candidates areremoved from the merging candidates. In Step S2003, the total number ofthe merging candidates after the removing is set as the size of themerging candidate list. In Step S2004, the merging candidate index to beused in decoding of a current block is decoded from a bitstream usingthe size of the merging candidate list. In Step S2005, the current blockis decoded by generating a prediction picture using the mergingcandidate indicated by the decoded merging candidate index.

FIG. 8 shows syntax for attaching a merging candidate index to abitstream. In FIG. 8 , merge_idx represents a merging candidate index,and merge_flag represents a merging flag. NumMergeCand represents thesize of a merging candidate list. NumMergeCand is set at the totalnumber of merging candidates after unusable-for-merging candidates andidentical candidates are removed from the merging candidates.

In the merging mode, when identical candidates are removed from mergingcandidates, a merging candidate index cannot be correctly decoded due toa discrepancy in bit sequence assigned to merging candidate indicesbetween a picture coding apparatus and a picture decoding apparatus.Such a discrepancy may occur when, for example, there is a difference inthe total number of merging candidates between the picture codingapparatus and the picture decoding apparatus.

Use of merging candidate lists having a fixed size has been discussed asa solution to the problem.

When the total number of merging candidates is equivalent to the size ofa merging candidate list, it is more likely that the merging candidatelist has a merging candidate including a motion vector for accurateprediction. It is therefore possible to achieve increased codingefficiency.

On the other hand, when the size of merging candidate lists is fixed,the total number of merging candidates after removing of identicalcandidates may be smaller than the size. In such a case, it is lesslikely that the merging candidate list has a merging candidate includinga motion vector for accurate prediction. This may lead to decrease incoding efficiency.

In one general aspect, the techniques disclosed here feature a picturecoding method which is a method for coding a picture on a block-by-blockbasis to generate a bitstream and includes: performing a firstderivation process for deriving a first merging candidate which includesa candidate set of a prediction direction, a motion vector, and areference picture index for use in coding of a current block; performinga second derivation process for deriving a second merging candidatewhich includes a candidate set of a prediction direction, a motionvector, and a reference picture index for use in the coding of thecurrent block, the second derivation process being different from thefirst derivation process; selecting a merging candidate to be used inthe coding of the current block from among the first merging candidateand the second merging candidate; and attaching an index for identifyingthe selected merging candidate to the bitstream, wherein in theperforming of a first derivation process, the first derivation processis performed so that a total number of the first merging candidates doesnot exceed a predetermined number, and the second derivation process isperformed when the total number of the first merging candidates is lessthan a predetermined maximum number of merging candidates.

With this, it is possible to perform the first derivation process sothat the total number of first merging candidates does not exceed apredetermined number. The total number of first merging candidates isthus controlled, and the variety of merging candidates therebyincreases. As a result, coding efficiency increases.

For example, the picture coding method may further include performing athird derivation process for deriving a third merging candidate whichincludes a candidate set of a prediction direction, a motion vector, anda reference picture index for use in the coding of the current block,the third derivation process being different from the first derivationprocess and the second derivation process, wherein the second derivationprocess is performed when the total number of the first mergingcandidates and third merging candidates is less than the predeterminedmaximum number of merging candidates, and in the selecting, the mergingcandidate to be used in the coding of the current block is selected fromamong the first merging candidate, the second merging candidate, and thethird merging candidate.

With this, it is possible to further perform the third derivationprocess in which a method different from methods used in the firstderivation process and the second derivation process is used. Thevariety of merging candidates thus further increases, and codingefficiency thereby increases.

For example, in the performing of a third derivation process, aplurality of the third merging candidates may be derived by performingthe third derivation process, and in the performing of a firstderivation process, the first derivation process may be a process forderiving, as the first merging candidate, a bi-predictive mergingcandidate which is a combination of two sets each including a predictiondirection, a motion vector, and a reference picture index and includedin the third merging candidates.

With this, it is possible to derive a bi-predictive first mergingcandidate by making a combination from a plurality of third mergingcandidates. A new bi-predictive first merging candidate can be thusderived even when none of the plurality of third merging candidates is abi-predictive merging candidate. As a result, the variety of mergingcandidates is increased, and coding efficiency thereby increases.

For example, in the performing of a third derivation process, the thirdderivation process may be a process for deriving the third mergingcandidate using a set of a prediction direction, a motion vector, and areference picture index which are used as a set for coding a blockspatially or temporally neighboring the current block.

With this, it is possible to derive a third merging candidate using aset of a prediction direction, a motion vector, and a reference pictureindex used for coding of a block spatially or temporally neighboring thecurrent block. The third merging candidate derived in this manner isreliable, and coding efficiency therefore increases.

For example, the second derivation process may be repeatedly performeduntil a total number of the first merging candidates, second mergingcandidates, and third merging candidates reaches the predeterminedmaximum number of merging candidates.

With this, it is possible to repeat the second derivation process untilthe total number of second merging candidates and third mergingcandidates reaches the predetermined maximum number of mergingcandidates. Merging candidates are thus derived to the maximum number,and coding efficiency therefore increases.

For example, in the performing of a second derivation process, thesecond derivation process may be a process for deriving, as the secondmerging candidate, a merging candidate including a motion vector whichis a zero vector.

With this, it is possible to derive a second merging candidate having azero vector as a motion vector. The merging candidate derived in thismanner is reliable when the current block is a stationary region, andcoding efficiency therefore increases.

For example, the predetermined number may depend on a maximum number ofthe first merging candidates to be derived using the first derivationprocess.

With this, it is possible to derive a first merging candidate using, asa predetermined number, a number dependent on the total number of firstmerging candidates which can be derived by the first derivation process.A first merging candidate is thus derived using an appropriatepredetermined number so that the variety of merging candidates mayincrease, and coding efficiency therefore increases.

For example, the picture coding method may further include switching acoding process between a first coding process conforming to a firststandard and a second coding process conforming to a second standard;and attaching, to the bitstream, identification information indicatingeither the first standard or the second standard to which the codingprocess after the switching conforms, wherein when the coding processafter the switching is the first coding process, the first codingprocess is performed by performing the first derivation process, thesecond derivation process, the selecting, and the attaching.

With this, it is possible to switchably perform the first coding processconforming to the first standard and the second coding processconforming to the second standard.

Furthermore, in one general aspect, the techniques disclosed herefeature a picture decoding method which is a method for decoding, on ablock-by-block basis, a coded image included in a bitstream, andincludes: performing a first derivation process for deriving a firstmerging candidate which includes a candidate set of a predictiondirection, a motion vector, and a reference picture index for use indecoding of a current block; performing a second derivation process forderiving a second merging candidate which includes a candidate set of aprediction direction, a motion vector, and a reference picture index foruse in the decoding of the current block, the second derivation processbeing different from the first derivation process; obtaining an indexfrom the bitstream; and selecting, based on the obtained index, amerging candidate to be used in the decoding of the current block fromamong the first merging candidate and the second merging candidate,wherein in the performing of a first derivation process, the firstderivation process is performed so that a total number of the firstmerging candidates does not exceed a predetermined number, and thesecond derivation process is performed when the total number of thefirst merging candidates is less than a predetermined maximum number ofmerging candidates.

With this, it is possible to perform the first derivation process sothat the total number of first merging candidates does not exceed apredetermined number. The total number of first merging candidates isthus controlled, and the variety of merging candidates therebyincreases. As a result, a bitstream coded with increased codingefficiency can be appropriately decoded.

For example, the picture decoding method may further include performinga third derivation process for deriving a third merging candidate whichincludes a candidate set of a prediction direction, a motion vector, anda reference picture index for use in the coding of the current block,the third derivation process being different from the first derivationprocess and the second derivation process, performing a third derivationprocess for deriving a third merging candidate which includes acandidate set of a prediction direction, a motion vector, and areference picture index for use in the coding of the current block, thethird derivation process being different from the first derivationprocess and the second derivation process, wherein the second derivationprocess is performed when the total number of the first mergingcandidates and third merging candidates is less than the predeterminedmaximum number of merging candidates, and in the selecting, the mergingcandidate to be used in the decoding of the current block is selectedfrom among the first merging candidate, the second merging candidate,and the third merging candidate.

With this, it is possible to further possible to derive a third mergingcandidate by performing the third derivation process in which a methoddifferent from methods used in the first derivation process and thesecond derivation process is used. The variety of merging candidatesthus further increases, and therefore a bitstream coded with increasedcoding efficiency can be appropriately decoded.

For example, in the performing of a third derivation process, aplurality of the third merging candidates may be derived by performingthe third derivation process, and in the performing of a firstderivation process, the first derivation process may be a process forderiving, as the first merging candidate, a bi-predictive mergingcandidate which is a combination of two sets each including a predictiondirection, a motion vector, and a reference picture index and includedin the third merging candidates.

With this, it is possible to derive a bi-predictive first mergingcandidate by making a combination from a plurality of third mergingcandidates. A new bi-predictive first merging candidate can be thusderived even when none of the plurality of third merging candidates is abi-predictive merging candidate. As a result, the variety of mergingcandidates is thus increased, and therefore a bitstream coded withincreased coding efficiency can be appropriately decoded.

For example, in the performing of a third derivation process, the thirdderivation process may be a process for deriving the third mergingcandidates using a set of a prediction direction, a motion vector, and areference picture index which are used as a set in decoding a blockspatially or temporally neighboring the current block.

With this, it is possible to derive a third merging candidate using aset of a prediction direction, a motion vector, and a reference pictureindex used for coding of a block spatially or temporally neighboring thecurrent block. The third merging candidate derived in this manner isreliable, and therefore a bitstream coded with increased codingefficiency can be appropriately decoded.

For example, the second derivation process may be repeatedly performeduntil a total number of the first merging candidates, second mergingcandidates, and third merging candidates reaches the predeterminedmaximum number of merging candidates.

With this, it is possible to repeat the second derivation process untilthe total number of second merging candidates and the third mergingcandidates reaches the predetermined maximum number of mergingcandidates. Merging candidates are thus derived to the maximum number,and therefore a bitstream coded with increased coding efficiency can beappropriately decoded.

For example, in the performing of a second derivation process, thesecond derivation process may be a process for deriving, as the secondmerging candidate, a merging candidate including a motion vector whichis a zero vector.

With this, it is possible to derive a second merging candidate having azero vector as a motion vector. The merging candidate derived in thismanner is reliable when the current block is a stationary region, andtherefore a bitstream coded with increased coding efficiency can beappropriately decoded.

For example, the predetermined number may depend on a maximum number ofthe first merging candidates to be derived using the first derivationprocess.

With this, it is possible to derive a first merging candidate using, asa predetermined number, a number dependent on the total number of firstmerging candidates which can be derived by the first derivation process.A first merging candidate is thus derived using an appropriatepredetermined number so that the variety of merging candidates may beincreased, and therefore a bitstream coded with increased codingefficiency can be appropriately decoded.

For example, the picture decoding method may further include: switchinga decoding process between a first decoding process conforming to afirst standard and a second decoding process conforming to a secondstandard, according to identification information attached to thebitstream and indicating either the first standard or the secondstandard, wherein when the decoding process after the switching is thefirst decoding process, the first decoding process is performed byperforming the first derivation process, the second derivation process,the obtaining, and the selecting.

With this, it is possible to switchably perform the first coding processconforming to the first standard and the second coding processconforming to the second standard.

These general and specific aspects can be implemented as a system, amethod, an integrated circuit, a computer program, a computer-readablerecording medium such as a CD-ROM, or as any combination of a system, amethod, an integrated circuit, a computer program, and acomputer-readable recording medium.

Exemplary embodiments will be described below with reference to thedrawings.

Each of the exemplary embodiments described below shows a general orspecific example. The numerical values, shapes, materials, structuralelements, the arrangement and connection of the structural elements,steps, the processing order of the steps, etc. shown in the followingexemplary embodiments are mere examples, and therefore do not limit thescope of the appended Claims and their equivalents. Therefore, among theconstituent elements in the following exemplary embodiments, constituentelements not recited in any one of the independent claims defining themost generic part of the inventive concept are described as structuralelements included as appropriate.

Embodiment 1

FIG. 9 is a block diagram showing a configuration of a picture codingapparatus 100 according to Embodiment 1. The picture coding apparatus100 codes a picture on a block-by-block basis to generate a bitstream.As shown in FIG. 9 , the picture coding apparatus 100 includes a mergingcandidate derivation unit 110, a prediction control unit 120, and acoding unit 130.

The merging candidate derivation unit 110 derives merging candidates.Then, the merging candidate derivation unit 110 generates a mergingcandidate list in which each of the derived merging candidates isassociated with an index for identifying the merging candidate(hereinafter referred to as merging candidate index). Specifically, themerging candidate derivation unit 110 includes a third derivation unit111, a first derivation unit 112, and a second derivation unit 113 asshown in FIG. 9 .

The third derivation unit 111 performs a third derivation process inwhich a merging candidate is derived using a third derivation method.The merging candidate derived using the third derivation process ishereinafter referred to as a third merging candidate. Then, the thirdderivation unit 111 registers the third merging candidate in the mergingcandidate list in association with a merging candidate index.

Specifically, the third derivation unit 111 performs, as the thirdderivation process, a process for deriving a third merging candidateusing, for example, a set of a prediction direction, a motion vector,and a reference picture index used for coding of a block spatially ortemporally neighboring a current block. Third merging candidate derivedfrom spatially neighboring blocks in this manner are referred to asspatial merging candidates, and third merging candidates derived fromtemporally neighboring blocks are referred to as temporal mergingcandidates.

The spatially neighboring block is a block within a picture includingthe current block and neighbors the current block. Specifically, theneighboring blocks A to D shown in FIG. 3 are examples of the spatiallyneighboring block.

The spatially neighboring block is not limited to the neighboring blocksA to D shown in FIG. 3 . Examples of the spatially neighboring block mayfurther include blocks neighboring any of the neighboring blocks A to D.

The temporally neighboring block is a block which is within a picturedifferent from a picture including the current block and corresponds tothe current block. Specifically, a co-located block is an example of thetemporally neighboring block.

The temporally neighboring block is not limited to a block located in aposition which is the same as the position of the current block in therespective picture (co-located block). For example, the temporallyneighboring block may be a block neighboring the co-located block.

The third derivation unit 111 may perform the third derivation processin which a merging candidate is derived using a method other than thethird derivation method. In other words, the third derivation unit 111need not perform the process for deriving a spatial merging candidate ora temporal merging candidate as the third derivation process.

The first derivation unit 112 performs a first derivation process forderiving a merging candidate, using a first derivation method which isdifferent from the third derivation method. The merging candidatederived using the first derivation process is hereinafter referred to asa first merging candidate. The first derivation unit 112 performs thefirst derivation process so that the total number of first mergingcandidates does not exceed a predetermined number. Then, the firstderivation unit 112 registers the first merging candidate in the mergingcandidate list in association with a merging candidate index.

The predetermined number is a maximum number of first mergingcandidates. The predetermined number may be fixed or variable. Forexample, the predetermined number may be set depending on the totalnumber of merging candidates which can be derived using the firstderivation process. Specifically, the first derivation unit 112 may setthe predetermined number depending on, for example, the total number ofthird merging candidates or the total number of referable pictures.Because of dependency of the predetermined number on the total number ofmerging candidates which can be derived using the first derivationprocess, the variety of merging candidates can be increased by derivingfirst merging candidates using an appropriate predetermined number, andcoding efficiency thereby increases.

Specifically, the first derivation unit 112 performs, as the firstderivation process, a process for deriving, for example, a bi-predictivemerging candidate as a first merging candidate by making a combinationof sets each including a prediction direction, a motion vector, and areference picture index. The sets are included in the third mergingcandidates. Merging candidates derived in this manner are hereinafterreferred to as combined merging candidates. The process for deriving acombined merging candidate will be described in detail in Embodiment 6.

The first derivation unit 112 may perform the first derivation processin which a merging candidate is derived using a method other than thefirst derivation method. In other words, the first derivation unit 112may perform, as the first derivation process, a process other than theprocess for deriving a combined merging candidate.

The second derivation unit 113 performs a second derivation process forderiving a merging candidate, using a second derivation method when thetotal number of first merging candidates and third merging candidates issmaller than a predetermined maximum number of merging candidates. Thesecond derivation method is different from the first derivation methodand the third derivation method. The merging candidate derived using thesecond derivation process is hereinafter referred to as a second mergingcandidate. Then, the second derivation unit 113 registers the secondmerging candidate in the merging candidate list in association with amerging candidate index.

Specifically, the second derivation unit 113 performs, as the secondderivation process, a process for deriving, for example, a mergingcandidate including a motion vector which is a zero vector. Mergingcandidates derived in this manner are hereinafter referred to as zeromerging candidates. The process for deriving a zero merging candidatewill be described in detail in Embodiment 5.

The second derivation unit 113 may perform the second derivation processin which a merging candidate is derived using a method other than thesecond derivation method. In other words, the second deriving unit 113need not perform the process for deriving a zero merging candidate asthe second derivation process.

The predetermined maximum number of merging candidates is a numberprovided in a standard, for example. Optionally, the predeterminedmaximum number of merging candidates may be determined according to, forexample, features of a current picture. In this case, the determinedmaximum number may be attached to a bitstream.

The prediction control unit 120 selects a merging candidate to be usedfor coding a current block from the first to third merging candidates.In other words, the prediction control unit 120 selects a mergingcandidate to be used for coding a current block from the mergingcandidate list.

The coding unit 130 attaches an index for identifying the selectedmerging candidate (merging candidate index) to a bitstream. For example,the coding unit 130 codes an index using the total number of first tothird merging candidates (total number of merging candidates), andattaches the coded index to a bitstream. Then, the coding unit 130attaches the coded index to a bitstream.

Optionally, the coding unit 130 may code an index using not the totalnumber of first to third merging candidates but, for example, apredetermined maximum number of merging candidates. Specifically, thecoding unit 130 may determine a bit sequence assigned to the value of anindex using a predetermined maximum number of merging candidates asshown in FIG. 5 and code the determined bit sequence by variable-lengthcoding. By doing this, the coding unit 130 can code an indexindependently of the total number of actually derived mergingcandidates. Therefore, even when information necessary for derivation ofa merging candidate (for example, information on a co-located block) islost, an index can be still decoded and error resistance is therebyenhanced. Furthermore, an index can be decoded independently of thetotal number of actually derived merging candidates. In other words, anindex can be decoded without waiting for derivation of mergingcandidates. In other words, a bitstream can be generated with whichderiving of merging candidates and decoding of indices can be performedin parallel.

Operations of the picture coding apparatus 100 in the above-describedconfiguration will be described below.

FIG. 10A is a flowchart showing processing operations of the picturecoding apparatus 100 according to Embodiment 1.

First, the merging candidate derivation unit 110 derives mergingcandidates (S110), and registers the derived merging candidates in amerging candidate list.

Next, the prediction control unit 120 selects a merging candidate to beused for coding a current block from the first to third mergingcandidates (S120). For example, the prediction control unit 120 selects,from the derived merging candidates, a merging candidate which minimizescost indicating the amount of code for the current block and others.

Next, the coding unit 130 attaches an index for identifying the selectedmerging candidate to a bitstream (S130). Furthermore, the coding unit130 generates inter-prediction picture of the current block byperforming inter prediction using the selected merging candidate. Inputpicture data is coded using inter-prediction picture generated in thismanner.

Step S110 in FIG. 10A will be described in detail below with referenceto FIG. 10B and FIG. 11 .

FIG. 10B is a flowchart of the deriving of merging candidates accordingto Embodiment 1. FIG. 11 shows an example of the merging candidate listgenerated by the picture coding apparatus 100 according to Embodiment 1.For FIG. 11 , it is assumed that a predetermined maximum number ofmerging candidates is five, and a predetermined number is two.

First, the third derivation unit 111 performs the third derivationprocess (S111). Note that a third merging candidate is not alwaysderived in Step S111. For example, the third derivation unit 111 derivesno third merging candidate by performing the third derivation processwhen a third merging candidate to be derived as a result of the thirdderivation process presently performed is identical to a previouslyderived third merging candidate. Here, one merging candidate beingidentical to another merging candidate means that the sets eachincluding a prediction direction, a motion vector, and a referencepicture index and included in the respective merging candidates areidentical to each other. In other examples, the third derivation unit111 does not derive a third merging candidate from a block spatially ortemporally neighboring a current block when the block is (1) a blockcoded by intra prediction, (2) a block outside a slice including thecurrent block or outside the boundary of a picture including the currentblock, or (3) a block yet to be coded.

Next, the third derivation unit 111 determines whether or not to end thethird derivation process (S112). For example, to determine whether ornot to end the third derivation process, the third derivation unit 111determines whether the third derivation process has been performed forall predetermined neighboring blocks.

When the third derivation unit 111 determines not to end the thirdderivation process (S112, No), the third derivation unit 111 performsthe third derivation process again (S111).

Referring to FIG. 11 , two third merging candidates (a spatial mergingcandidate and a temporal merging candidate) are derived from theneighboring blocks A to D and a co-located block. The third mergingcandidates are provided with merging candidate indices having values of“0” and “1”, respectively.

When the third derivation unit 111 determines to end the thirdderivation process (S112, Yes), the first derivation unit 112 performsthe first derivation process (S113). Next, the first derivation unit 112determines whether or not the total number of first merging candidatesderived using the first derivation process is below a predeterminednumber (S114).

When the total number of first merging candidates is below thepredetermined number (S114, Yes), the first derivation unit 112 performsthe first derivation process again (S113). In other words, the firstderivation unit 112 performs the first derivation process so that thetotal number of first merging candidates does not exceed a predeterminednumber.

Referring to FIG. 11 , two first merging candidates (combined mergingcandidates) are derived by making combinations from the two thirdmerging candidates. The first merging candidates are provided withmerging candidate indices having values of “2” and “3”, which are largerthan those of the third merging candidates.

When the total number of first merging candidates is not below thepredetermined number (S114, No), the second derivation unit 113 performsthe second derivation process (S115). Next, the second derivation unit113 determines whether or not the total number of first to third mergingcandidates is below a predetermined maximum number of merging candidates(S116).

When the total number of first to third merging candidates is below thepredetermined maximum number (S116, Yes), the second derivation unit 113performs the second derivation process again (S115). In other words, thesecond derivation unit 113 repeats the second derivation process untilthe total number of first to third merging candidates reaches thepredetermined maximum number of merging candidates.

Referring to FIG. 11 , the total number of first and third mergingcandidates is four, and the predetermined maximum number of mergingcandidates is five, and therefore one second merging candidate (zeromerging candidate) is derived. The second merging candidate is providedwith a merging candidate index having a value of “4”, which is largerthan those of the first and third merging candidates.

When the total number of first to third merging candidates is not belowthe maximum number (S116, No), the process proceeds to Step S120 shownin FIG. 10A.

In this manner, the picture coding apparatus 100 according to Embodiment1 performs the first derivation process so that the total number offirst merging candidates does not exceed a predetermined number. Thepicture coding apparatus 100 thereby controls the total number of firstmerging candidates to increase the variety of merging candidates. As aresult, the picture coding apparatus 100 can code pictures withincreased efficiency.

Furthermore, the second derivation unit 113 can repeat the secondderivation process until the total number of first to third mergingcandidates reaches a predetermined maximum number of merging candidates.The second derivation unit 113 thereby derives merging candidates to themaximum number of merging candidates, and coding efficiency thereforeincreases.

Furthermore, merging candidates can be derived in descending order ofreliability by performing the deriving in an order of spatial ortemporal merging candidates as third merging candidates, combinedmerging candidates as first merging candidates, and zero mergingcandidates as second merging candidates as shown in FIG. 11 . It istherefore more likely that derived merging candidates are more reliable.

The merging candidate derivation unit may assign merging candidateindices to merging candidates in such a manner that the mergingcandidate indices of combined merging candidates (first mergingcandidates) are larger than those of the spatial or temporal mergingcandidates (third merging candidates) and the merging candidate indicesof zero merging candidates (second merging candidates) are larger thanthose of the combined merging candidates (first merging candidates) asshown in FIG. 11 . The merging candidate derivation unit 110 therebyassigns indices having smaller values to merging candidates which aremore likely to be selected, and therefore the amount of codes assignedto merging candidate indices is saved.

Note that the first to third merging candidates are not limited tocombined merging candidates, zero merging candidates, or spatial ortemporal merging candidates. Note also that the values of the indicesassigned to the first to third merging candidates are not limited to thevalues of the indices shown in FIG. 11 .

Note that the picture coding apparatus 100 need not derive third mergingcandidates in Embodiment 1. In other words, the merging candidatederivation unit 110 may not include the third derivation unit 111 shownin FIG. 9 . In this case, the picture coding apparatus 100 skips StepS111 and Step S112 in the process shown in FIG. 10B. The process isperformed without using third merging candidates in Step S113 to StepS116. For example, in Step S115, the second derivation unit 113determines whether or not the total number of first merging candidatesis below a predetermined maximum number of merging candidates.

For example, the picture coding apparatus 100 may further derive fourthmerging candidates. For example, the merging candidate derivation unit110 may derive a scaling merging candidate as a fourth merging candidatewhen it is impossible to derive as many second merging candidates as tomake the total number of first to third merging candidates equal to amaximum number of merging candidates. The process for deriving a scalingmerging candidate will be described in detail in Embodiment 7. Note alsothat in Embodiment 1, the second derivation unit need not repeat thesecond derivation process until the total number of first to thirdmerging candidates reaches a predetermined maximum number of mergingcandidates. For example, the total number of first to third mergingcandidates is not equal to a predetermined maximum number of mergingcandidates when the difference between the predetermined maximum numberof merging candidates and the total number of first to third mergingcandidates is larger than the total number of second merging candidateswhich can be derived using the second derivation process.

Embodiment 2

Embodiment 2 will be described below.

FIG. 12 is a block diagram showing a configuration of a picture decodingapparatus 200 according to Embodiment 2. The picture decoding apparatus200 is an apparatus corresponding to the picture coding apparatus 100according to Embodiment 1. Specifically, for example, the picturedecoding apparatus 200 decodes, on a block-by-block basis, codedpictures included in a bitstream generated by the picture codingapparatus 100 according to Embodiment 1. As shown in FIG. 12 , thepicture decoding apparatus 200 includes a merging candidate derivationunit 210, a decoding unit 220, and a prediction control unit 230.

As with the merging candidate derivation unit 110 in Embodiment 1, themerging candidate derivation unit 210 derives merging candidates. Themerging candidate derivation unit 210 generates a merging candidate listin which each of the derived merging candidates is associated with amerging candidate index. Specifically, the merging candidate derivationunit 210 includes a third derivation unit 211, a first derivation unit212, and a second derivation unit 213 as shown in FIG. 12 .

The third derivation unit 211 performs the same process as the processperformed by the third derivation unit 111 in Embodiment 1. In otherwords, the third derivation unit 211 performs the third derivationprocess for deriving a third merging candidate using the thirdderivation method. Then, the third derivation unit 111 registers thethird merging candidate in the merging candidate list in associationwith a merging candidate index.

Specifically, the third derivation unit 211 performs, as the thirdderivation process, a process for deriving a third merging candidateusing, for example, a set of a prediction direction, a motion vector,and a reference picture index used for decoding of a block spatially ortemporally neighboring a current block.

The first derivation unit 212 performs the same process as the processperformed by the first derivation unit 112 in Embodiment 1. In otherwords, the first derivation unit 212 performs the first derivationprocess for deriving a first merging candidate, using the firstderivation method. The first derivation unit 212 performs the firstderivation process so that the total number of first merging candidatesdoes not exceed a predetermined number. Then, the first derivation unit212 registers the first merging candidate in the merging candidate listin association with a merging candidate index.

Specifically, the first derivation unit 212 performs, as the firstderivation process, a process for deriving, for example, a bi-predictivemerging candidate as a first merging candidate by making a combinationof sets each including a prediction direction, a motion vector, and areference picture index. The sets are included the third mergingcandidates.

The term “bi-predictive” means prediction with reference to the firstreference picture list and the second reference picture list. Note thatbeing “bi-predictive” does not always involve references both to atemporally preceding reference picture and to a temporally followingreference picture. In other words, a bi-predictive merging candidate maybe coded and decoded with reference to reference pictures in the samedirection (preceding reference pictures or following referencepictures).

The second derivation unit 213 performs the same process as the processperformed by the second derivation unit 113 in Embodiment 1. In otherwords, the second derivation unit 213 performs a second derivationprocess for deriving a second merging candidate, using the secondderivation method when the total number of first merging candidates andthird merging candidates is smaller than a predetermined maximum numberof merging candidates. Then, the second derivation unit 213 registersthe second merging candidate in the merging candidate list inassociation with a merging candidate index.

Specifically, the second derivation unit 213 performs, as the secondderivation process, a process for deriving, for example, a mergingcandidate including a motion vector which is a zero vector (zero mergingcandidate). In this case, the second derivation unit 213 performs thesecond derivation process using indices of referable picturessequentially as reference picture indices included in zero mergingcandidates.

The decoding unit 220 obtains an index for identifying a mergingcandidate (merging candidate index) from a bitstream. For example, thedecoding unit 220 obtains a merging candidate index by decoding, usingthe total number of first to third merging candidates or a predeterminedmaximum number of merging candidates, a merging candidate index codedand attached to a bitstream.

The prediction control unit 230 selects, using the index obtained by thedecoding unit 220, a merging candidate to be used for decoding a currentblock from the first to third merging candidates. In other words, theprediction control unit 230 selects a merging candidate from the mergingcandidate list. The selected merging candidate is to be used forgenerating a prediction picture of a current block to be decoded.

Operations of the picture decoding apparatus 200 in the above-describedconfiguration will be described below.

FIG. 13A is a flowchart showing processing operations of the picturedecoding apparatus 200 according to Embodiment 2.

First, the merging candidate derivation unit 210 derives mergingcandidates in the same manner as in Step S110 in FIG. 10A (S210).

Next, the decoding unit 220 obtains a merging candidate index from abitstream (S220). For example, the decoding unit 220 obtains a mergingcandidate index by decoding a coded merging candidate index using thetotal number of first to third merging candidates (the number of mergingcandidates).

Optionally, the decoding unit 220 may obtain a merging candidate indexby decoding a coded merging candidate index using a predeterminedmaximum number of merging candidates. In this case, the decoding unit220 may obtain a merging candidate index (S220) before the deriving ofmerging candidates (S210). Alternatively, the decoding unit 220 mayobtain a merging candidate index (S220) in parallel with the deriving ofmerging candidates (S210).

Next, the prediction control unit 230 selects, using the obtainedmerging candidate index, a merging candidate to be used for decoding acurrent block from the first to third merging candidates (S230).

Step S210 in FIG. 13A will be described in detail below with referenceto FIG. 13B.

FIG. 13B is a flowchart showing the deriving of merging candidatesaccording to Embodiment 2.

First, the third derivation unit 111 performs the third derivationprocess in the same manner as in Step S111 in FIG. 10B (S211). Next, thethird derivation unit 211 determines whether or not to end the thirdderivation process (S212). When the third derivation unit 211 determinesnot to end the third derivation process (S212, No), the third derivationunit 211 performs the third derivation process again (S211).

When the third derivation unit 211 determines to end the thirdderivation process (S212, Yes), the first derivation unit 212 performsthe first derivation process in the same manner as in Step S113 in FIG.10B (S213). Next, the first derivation unit 212 determines whether ornot the total number of first merging candidates derived using the firstderivation process is below a predetermined number (S214).

When the total number of first merging candidates is not below thepredetermined number (S214, No), the second derivation unit 213 performsthe second derivation process in the same manner as in Step S115 in FIG.10B (S215). Next, the second derivation unit 213 determines whether ornot the total number of first to third merging candidates is below apredetermined maximum number of merging candidates (S216).

When the total number of first to third merging candidates is below thepredetermined maximum number (S216, Yes), the second derivation unit 213performs the second derivation process again (S215). In other words, thesecond derivation unit 213 repeats the second derivation process untilthe total number of first to third merging candidates reaches thepredetermined maximum number of merging candidates.

When the total number of first to third merging candidates is not belowthe maximum number (S216, No), the process proceeds to Step S220 shownin FIG. 13A.

In this manner, the picture decoding apparatus 200 according toEmbodiment 2 performs the first derivation process so that the totalnumber of first merging candidates does not exceed a predeterminednumber. The picture decoding apparatus 200 thereby controls the totalnumber of first merging candidates, and the variety of mergingcandidates thereby increases. As a result, the picture decodingapparatus 200 can appropriately decode a bitstream coded with increasedcoding efficiency.

Furthermore, the second derivation unit 213 can repeat the secondderivation process until the total number of first to third mergingcandidates reaches a predetermined maximum number of merging candidates.The second derivation unit 213 thereby derives merging candidates to themaximum number of merging candidates, and coding efficiency thereforeincreases. The increase allows the picture decoding apparatus 200 toappropriately decode a bitstream coded with increased coding efficiency.

Note that the picture decoding apparatus 200 need not derive thirdmerging candidates in Embodiment 2. In other words, the mergingcandidate derivation unit 210 may not include the third derivation unit211 shown in FIG. 12 . In this case, the picture decoding apparatus 200skips Step S211 and Step S212 in the process shown in FIG. 10B. Theprocess is performed without using third merging candidates in Step S213to Step S216. For example, in Step S215, the second derivation unit 213determines whether or not the total number of first merging candidatesis below a predetermined maximum number of merging candidates.

Embodiment 3

A picture coding apparatus according to Embodiment 3 will bespecifically described below with reference to drawings. The picturecoding apparatus according to Embodiment 3 is an example of possibleapplications of the picture coding apparatus according to Embodiment 1.

FIG. 14 is a block diagram showing a configuration of a picture codingapparatus 300 according to Embodiment 3. The picture coding apparatus300 codes a picture on a block-by-block basis to generate a bitstream.

As shown in FIG. 14 , the picture coding apparatus 300 includes asubtractor 301, an orthogonal transformation unit 302, a quantizationunit 303, an inverse-quantization unit 304, an inverse-orthogonaltransformation unit 305, an adder 306 a block memory 307, a frame memory308, an intra prediction unit 309, an inter prediction unit 310, aninter prediction control unit 311, a picture-type determination unit312, a switch 313, a merging candidate derivation unit 314, a colPicmemory 315, and a variable-length-coding unit 316.

The subtractor 301 subtracts, on a block-by-block basis, predictionpicture data from input picture data included in an input image sequenceto generate prediction error data.

The orthogonal transformation unit 302 transforms the generatedprediction error data from picture domain into frequency domain.

The quantization unit 303 quantizes the prediction error data in afrequency domain as a result of the transform.

The inverse-quantization unit 304 inverse-quantizes the prediction errordata quantized by the quantization unit 303.

The inverse-orthogonal-transformation unit 305 transforms theinverse-quantized prediction error data from frequency domain intopicture domain.

The adder 306 generates reconstructed picture data by adding, on ablock-by-block basis, prediction picture data and the prediction errordata inverse-quantized by the inverse-orthogonal-transformation unit305.

The block memory 307 stores the reconstructed picture data in units of ablock.

The frame memory 308 stores the reconstructed picture data in units of aframe.

The picture-type determination unit 312 determines in which of thepicture types of I-picture, B-picture, and P-picture the input picturedata is to be coded. Then, the picture-type determination unit 312generates picture-type information indicating the determined picturetype.

The intra prediction unit 309 generates intra prediction picture data ofa current block by performing intra prediction using reconstructedpicture data stored in the block memory 307 in units of a block.

The inter prediction unit 310 generates inter prediction picture data ofa current block by performing inter prediction using reconstructedpicture data stored in the frame memory 308 in units of a frame and amotion vector derived by a process including motion estimation. Forexample, when the merging mode is selected as a prediction mode to beused, the inter prediction unit 310 generates prediction picture data ofa current block by performing inter prediction using a mergingcandidate.

When a current block is coded using intra prediction, the switch 313outputs intra prediction picture data generated by the intra predictionunit 309 as prediction picture data of the current block to thesubtractor 301 and the adder 306. When a current block is coded usinginter prediction, the switch 313 outputs inter prediction picture datagenerated by the inter prediction unit 310 as prediction picture data ofthe current block to the subtractor 301 and the adder 306.

As with the merging candidate derivation unit 110 in Embodiment 1, themerging candidate derivation unit 314 derives merging candidates.Specifically, the merging candidate derivation unit 314 performsprocesses for deriving merging candidates (the first derivation processand the second derivation process) using at least two differentderivation methods (the first derivation method and the secondderivation method). For example, the merging candidate derivation unit314 derives merging candidates using neighboring blocks of a currentblock and colPic information stored in the colPic memory 315. The colPicinformation indicates information on a co-located block of the currentblock, such as a motion vector.

The merging candidate derivation unit 314 limits the total number offirst merging candidates derived using the first derivation method butdoes not limit the total number of second merging candidates derivedusing the second derivation method. In other words, the mergingcandidate derivation unit 314 derives first merging candidates so thatthe total number of first merging candidates does not exceed apredetermined number. When the total number of derived first mergingcandidates is less than the size of a merging candidate list, themerging candidate derivation unit 314 derives second merging candidatesuntil the total number of the derived first and second mergingcandidates becomes equivalent to the size of the merging candidate list.

In this manner, the total number of first merging candidates is limitedand the total number of second merging candidates is not limited. Themerging candidate derivation unit 314 can therefore derive a variety ofmerging candidates. Furthermore, the merging candidate derivation unit314 derives merging candidates until the total number of the derivedmerging candidates becomes equivalent to the size of the mergingcandidate list. The merging candidate list is therefore more likely toinclude a merging candidate having a motion vector for accurateprediction. The merging candidate derivation unit 314 therebycontributes to increase in coding efficiency.

Furthermore, the merging candidate derivation unit 314 assigns mergingcandidate indices to the derived merging candidates. Then, the mergingcandidate derivation unit 314 transmits the merging candidates and themerging candidate indices to the inter prediction control unit 311.Furthermore, the merging candidate derivation unit 314 transmits thetotal number of the derived merging candidates (the number of mergingcandidates) to the variable-length-coding unit 316.

The inter prediction control unit 311 selects, from a prediction mode inwhich a motion vector derived by motion estimation is used (motionestimation mode) and a prediction mode in which a merging candidate isused (merging mode), a prediction mode which provides the smallerprediction error. Furthermore, the inter prediction control unit 313transmits a merging flag indicating whether or not the selectedprediction mode is the merging mode to the variable-length-coding unit316. Furthermore, when the selected prediction mode is the merging mode,the inter prediction control unit 311 transmits a merging candidateindex corresponding to the selected merging candidate to thevariable-length-coding unit 316. Furthermore, the inter predictioncontrol unit 311 transmits colPic information including a motion vectorof the current block to the colPic memory 315.

The variable-length-coding unit 316 generates a bitstream by performingvariable-length coding on the quantized prediction error data, themerging flag, and the picture-type information. Furthermore, thevariable-length-coding unit 316 sets the total number of the derivedmerging candidates as the size of the merging candidate list. Then, thevariable-length-coding unit 316 performs variable-length coding on a bitsequence by assigning, according to the size of the merging candidatelist, a bit sequence to the merging candidate index to be used forcoding of the current block.

Operations of the picture coding apparatus 300 in the above-describedconfiguration will be described below.

FIG. 15 is a flowchart showing processing operations of the picturecoding apparatus 300 according to Embodiment 3.

In Step S310, the merging candidate derivation unit 314 derives mergingcandidates in the manner described in Embodiment 1.

In Step S320, the inter prediction control unit 311 selects a predictionmode based on comparison, using a method described later, betweenprediction error of a prediction picture generated using a motion vectorderived by motion estimation and prediction error of a predictionpicture generated using a merging candidate. The inter predictioncontrol unit 311 sets the merging flag to “1” when the selectedprediction mode is the merging mode, and sets the merging flag to “0”when otherwise. In Step S330, a determination is made as to whether ornot the value of the merging flag is “1” (that is, the selectedprediction mode is the merging mode).

When the result of the determination in Step S330 is true (Yes, S330),the variable-length-coding unit 316 attaches the merging flag to abitstream in Step S340. In Step S350, the variable-length-coding unit316 assigns a bit sequence according to the size of the mergingcandidate list as shown in FIG. 5 to the merging candidate index ofmerging candidates to be used for coding of the current picture. Then,the variable-length-coding unit 316 performs variable-length coding onthe assigned bit sequence.

When the result of the determination in Step S330 is false (S333, No),the variable-length-coding unit 316 attaches a merging flag andinformation for motion estimation vector mode to a bitstream in StepS360.

Note that in Step S350, the variable-length-coding unit 316 need notattach a merging candidate index to a bitstream when, for example, thesize of the merging candidate list is “1”. The amount of information onthe merging candidate index is thereby reduced.

FIG. 16 is a flowchart showing details of the process in Step S320 inFIG. 15 . Specifically, FIG. 16 illustrates a process for selecting amerging candidate. FIG. 16 will be described below.

In Step S321, the inter prediction control unit 311 initializes settingsfor the process. Specifically, the inter prediction control unit 311sets a merging candidate index at “0”, the minimum prediction error atthe prediction error (cost) in the motion vector estimation mode, and amerging flag at “0”. The cost is calculated using the following equationfor an R-D optimization model, for example.Cost=D+λR  (Equation 1)

In Equation 1, D denotes coding distortion. For example, D is the sum ofabsolute differences between original pixel values of a current block tobe coded and pixel values obtained by coding and decoding of the currentblock using a prediction picture generated using a motion vector. Rdenotes the amount of generated codes. For example, R is the amount ofcodes necessary for coding a motion vector used for generation of aprediction picture. λ denotes an undetermined Lagrange multiplier.

In Step S322, the inter prediction control unit 311 determines whetheror not the value of a merging candidate index is smaller than the totalnumber of merging candidates of a current block. In other words, theinter prediction control unit 311 determines whether or not there isstill any merging candidate on which the process from Step S323 to StepS325 has not been performed yet.

When the result of the determination in Step S322 is true (S322, Yes),in Step S323, the inter prediction control unit 311 calculates the costfor a merging candidate to which a merging candidate index is assigned.Then, in Step S324, the inter prediction control unit 311 determineswhether or not the calculated cost for the merging candidate is smallerthan the minimum prediction error.

When the result of the determination in Step S324 is true, (S324, Yes),the inter prediction control unit 311 updates the minimum predictionerror, the merging candidate index, and the value of the merging flag inStep S325. When the result of the determination in Step S324 is false(S324, No), the inter prediction control unit 311 does not update theminimum prediction error, the merging candidate index, or the value ofthe merging flag.

In Step S326, the inter prediction control unit 311 increments themerging candidate index by one, and repeats the process from Step S322to Step S326.

When the result of the determination in Step S322 is false (Step S322,No), that is, when there is no more merging candidate on which thisprocess has not been performed, the inter prediction control unit 311settles the values of the merging flag and the merging candidate indexin Step S327.

Note that in Embodiment 3, it is not always necessary in the mergingmode to attach a merging flag to a bitstream. For example, a mergingflag need not be attached to a bitstream when the merging mode isforcibly selected for a current block which satisfies a predeterminedcondition. This reduces the amount of information, and coding efficiencythereby increases.

Note that the picture coding apparatus according to Embodiment 3 is notlimited to the example described therein where the merging mode is usedin which a current block is coded using a prediction direction, a motionvector, and a reference picture index copied from a neighboring block ofthe current block. For example, a current block may be coded in skipmerging mode. In the skip merging mode, a current block is coded using amerging candidate as in the merging mode. When all items in predictionerror data are “0” for the current block, a skip flag is set at “1” andthe skip flag and a merging candidate index are attached to a bitstream.When prediction error includes an item which is not “0” for a currentblock, a skip flag is set at “0” and the skip flag, a merging flag, amerging candidate index, and the prediction error data are attached to abitstream.

Note that the picture coding apparatus according to Embodiment 3 is notlimited to the example described therein in which a current block iscoded using a merging candidate. For example, a motion vector in themotion vector estimation mode may be coded using a merging candidate.Specifically, a difference may be calculated by subtracting a motionvector of a merging candidate indicated by a merging candidate indexfrom a motion vector in the motion vector estimation mode. Then, thedifference and the merging candidate index are attached to a bitstream.Optionally, a difference may be calculated by scaling a motion vectorMV_Merge of a merging candidate using a reference picture indexRefIdx_ME in the motion vector estimation mode and a reference pictureindex RefIdx_Merge of the merging candidate as represented by Equation2, and subtracting a motion vector scaledMV_Merge of the mergingcandidate after the scaling from the motion vector in the motion vectorestimation mode. Then, the calculated difference and the mergingcandidate index are attached to a bitstream.scaledMV_Merge=MV_Merge×(POC(RefIdx_ME)−curPOC)/(POC(RefIdx_Merge)−curPOC)  (Equation 2)

Here, POC (RefIdx_ME) denotes the display order of reference pictureindicated by a reference picture index RefIdx_ME. POC (RefIdx_Merge)denotes the display order of a reference picture indicated by areference picture index RefIdx_Merge. curPOC denotes the display orderof a current picture to be coded.

Embodiment 4

Embodiment 4 will be described below.

FIG. 17 is a block diagram showing a configuration of a picture decodingapparatus 400 according to Embodiment 4. The picture decoding apparatus400 is an apparatus corresponding to the picture coding apparatus 300according to Embodiment 3. Specifically, for example, the picturedecoding apparatus 400 decodes, on a block-by-block basis, codedpictures included in a bitstream generated by the picture codingapparatus 300 according to Embodiment 3.

As shown in FIG. 17 , the picture decoding apparatus 400 includes avariable-length decoding unit 401, an inverse-quantization unit 402, aninverse-orthogonal-transformation unit 403, an adder 404, a block memory405, a frame memory 406, an intra prediction unit 407, an interprediction unit 408, an inter prediction control unit 409, a switch 410,a merging candidate derivation unit 411, and a colPic memory 412.

The variable-length-decoding unit 401 generates picture-typeinformation, a merging flag, and a quantized coefficient by performingvariable-length decoding on an input bitstream. Furthermore, thevariable-length-decoding unit 401 variable-length decodes a mergingcandidate index using the size of a merging candidate list.

The inverse-quantization unit 402 inverse-quantizes the quantizedcoefficient obtained by the variable-length decoding.

The inverse-orthogonal-transformation unit 403 generates predictionerror data by transforming an orthogonal transform coefficient obtainedby the inverse quantization from frequency domain into picture domain.

The block memory 405 stores, in units of a block, decoded picture datagenerated by adding prediction error data and prediction picture data.

The frame memory 406 stores decoded picture data in units of a frame.

The intra prediction unit 407 generates prediction picture data of acurrent block by performing intra prediction using the decoded picturedata stored in the block memory 405 in units of a block.

The inter prediction unit 408 generates prediction picture data of acurrent block by performing inter prediction using the decoded picturedata stored in the frame memory 406 in units of a frame. For example,when a merging flag is set to 1, the inter prediction unit 408 generatesprediction picture data of a current block by performing interprediction using a merging candidate.

The switch 410 outputs, as prediction picture data of a current block,intra prediction picture data generated by the intra prediction unit 407or inter prediction picture data generated by the inter prediction unit408 to the adder 404.

The merging candidate derivation unit 411 performs processes forderiving merging candidates (the first derivation process and the secondderivation process) using at least two different derivation methods (thefirst derivation method and the second derivation method) as inEmbodiment 3. For example, the merging candidate derivation unit 411derives merging candidates using neighboring blocks of a current blockand colPic information stored in the colPic memory 412. The colPicinformation indicates information on a co-located block of the currentblock, such as a motion vector.

The merging candidate derivation unit 411 limits the total number offirst merging candidates derived using the first derivation method butdoes not limit the total number of second merging candidate derivedusing the second derivation method. In other words, the mergingcandidate derivation unit 411 derives first merging candidates so thatthe total number of first merging candidates does not exceed apredetermined number. When the total number of derived first mergingcandidates is less than the size of a merging candidate list, themerging candidate derivation unit 411 derives second merging candidatesuntil the total number of the derived first and second mergingcandidates becomes equivalent to the size of the merging candidate list.

In this manner, the total number of first merging candidates is limitedand the total number of second merging candidates is not limited. Themerging candidate derivation unit 411 can therefore derive a variety ofmerging candidates. Furthermore, the merging candidate derivation unit411 derives merging candidates until the total number of derived mergingcandidates becomes equivalent to the size of the merging candidate list.The merging candidate list is therefore more likely to include a mergingcandidate having a motion vector for accurate prediction.

Furthermore, the merging candidate derivation unit 411 assigns mergingcandidate indices to the derived merging candidates. Then, the mergingcandidate derivation unit 411 transmits the merging candidates and themerging candidate indices to the inter prediction control unit 409.Furthermore, the merging candidate derivation unit 411 transmits thetotal number of the derived merging candidates (the number of mergingcandidates) to the variable-length-decoding unit 401.

The inter prediction control unit 409 causes the inter prediction unit408 to generate an inter prediction picture using information for motionvector estimation mode, when a decoded merging flag has a value of “0”.When a decoded merging flag has a value of “1”, the inter predictioncontrol unit 409 selects, based on a decoded merging candidate index, amerging candidate for inter prediction from the derived mergingcandidates. Then, the inter prediction control unit 409 causes the interprediction unit 408 to generate an inter prediction picture using theselected merging candidate. Furthermore, the inter prediction controlunit 409 transfers colPic information including the motion vector of thecurrent block to the colPic memory 412.

Finally, the adder 404 generates decoded picture data by addingprediction picture data and prediction error data.

FIG. 18 is a flowchart showing processing operations of the picturedecoding apparatus 400 according to Embodiment 4.

In Step S414, the variable-length-decoding unit 401 decodes a mergingflag.

When it is determined in Step S420 that the merging flag has a value of“1” (S420, Yes), a merging candidate is derived in Step S430 using thesame method as the method used in Step S310 in FIG. 15 .

In Step S440, the variable-length-decoding unit 401 performsvariable-length decoding on a merging candidate index from a bitstreamusing the size of a merging candidate list.

In Step S450, the inter prediction control unit 409 generates interprediction picture using a prediction direction, a motion vector, and areference picture index which are included in the merging candidateindicated the decoded merging index.

When it is determined in Step S420 that the merging flag has a value of“0” (S420, No), in Step S460, the inter prediction unit 408 generates aninter prediction picture using information for motion vector estimationmode decoded by the variable-length-decoding unit 401.

Optionally, when the total number of merging candidates (the size ofmerging candidate list) derived in Step S430 is “1”, a merging candidateindex may be assumed to be “0” instead of being decoded.

Embodiment 5

In Embodiment 5, a process for deriving a zero merging candidate will bedescribed in detail using drawings. The process for deriving a zeromerging candidate described herein is an example of the first derivationprocess or the second derivation process.

FIG. 19 is a flowchart showing the process for deriving a zero mergingcandidate according to Embodiment 5. Specifically, FIG. 19 shows part ofprocessing operations of the merging candidate derivation unit 110, 210,314, or 411 in Embodiments 1 to 4. In other words, FIG. 19 showsprocessing operations of the first derivation unit or the secondderivation unit.

In Step S501, the merging candidate derivation unit updates the value ofreference picture index refIdxL0 for the prediction direction 0 and thevalue of reference picture index refIdxL1 for the prediction direction 1which are to be used for deriving a zero merging candidate. Thereference picture indices refIdxL0 and refIdxL1 each have an initialvalue of “−1”, and are incremented by “+1” each time the process in StepS501 is performed.

Specifically, in the first cycle of the process for deriving a mergingcandidate, a zero merging candidate including a motion vector having avalue of zero (zero vector) and a reference picture index having a valueof 0 is added to a merging candidate list as a zero merging candidatefor stationary region. Next, in the second cycle of the process forderiving a merging candidate, a zero merging candidate including amotion vector having a value of zero (zero vector) and a referencepicture index having a value of 1 is added to a merging candidate list.

In Step S502, the merging candidate derivation unit determines whetherit is true or false that (i) the updated value of the reference pictureindex refIdxL0 for the prediction direction 0 is smaller than a maximumnumber of reference pictures in the reference picture list 0 for theprediction direction 0 and (ii) the updated value of the referencepicture index refIdxL1 for the prediction direction 1 is smaller than amaximum number of reference pictures in the reference picture list 1 forthe prediction direction 1.

When the result of the determination in Step S502 is true, (S502, Yes),the merging candidate derivation unit assigns a motion vector (0, 0) andthe reference picture index refIdxL0 to the motion vector and referencepicture index for the prediction direction 0 of the zero mergingcandidate in Step S503. Moreover, in Step S504, the merging candidatederivation unit assigns a motion vector (0, 0) and the reference pictureindex refIdxL1 to the motion vector and reference picture index for theprediction direction 1 of the zero merging candidate.

The merging candidate derivation unit thereby derives a bi-predictivezero merging candidate by the processes in Step S503 and Step S504. FIG.20 shows an example of a derived zero merging candidate.

In Step S505, the merging candidate derivation unit determines whetheror not the merging candidate list already includes a merging candidatewhich is identical in prediction direction, motion vector, and referencepicture index to the derived zero merging candidate. In other words, themerging candidate derivation unit determines whether or not the derivedzero merging candidate is an identical candidate.

When the result of Step S505 is false (S505, No), the merging candidatederivation unit registers the derived zero merging candidate in themerging candidate list in Step S506.

When the result of the determination in Step S502 is false (S502, No) orthe result of the determination in Step S505 is true (S505, Yes), themerging candidate derivation unit does not register the derived zeromerging candidate in the merging candidate list in Step S506.

The merging candidate derivation unit thereby derives a zero mergingcandidate which has a motion vector having zero values to referablereference pictures. Next, the merging candidate derivation unit adds thederived zero merging candidate to the merging candidate list. Thepicture coding apparatus thus can increase efficiency of coding inmerging mode especially when a current block to be coded is a stationaryregion.

Note that the picture coding apparatus is not limited to the exampledescribed in Embodiment 5, in which a bi-predictive zero mergingcandidate is derived using a motion vector having zero values, areference picture index for the prediction direction 0, and a referencepicture index for the prediction direction 1. For example, the mergingcandidate derivation unit may derive a zero merging candidate for theprediction direction 0 using a motion vector having zero values and areference picture index for the prediction direction 0. Similarly, themerging candidate derivation unit may derive a zero merging candidatefor the prediction direction 1 using a motion vector having zero valuesand a reference picture index for the prediction direction 1.

Note that the picture coding apparatus is not limited to the exampledescribed in Embodiment 5, in which zero merging candidates are derivedusing reference picture indices starting from the value of 0 andincremented by +1. For example, the merging candidate derivation unitmay derive zero merging candidates using reference picture indices inascending order of distance from a current picture to reference picturesin display order.

Note that the picture coding apparatus is not limited to the exampledescribed in Embodiment 5, in which the merging candidate derivationunit determines in Step S505 in FIG. 19 whether or not a zero mergingcandidate is an identical candidate. For example, the merging candidatederivation unit may skip the determination in Step S505. This reducescomputational complexity in deriving a merging candidate for the mergingcandidate derivation unit.

The merging candidate derivation unit according to Embodiment 5 therebyderives, as a first merging candidate or a second merging candidate, amerging candidate including zero vectors which are motion vectors for astationary region, and coding efficiency therefore increases. Morespecifically, the merging candidate derivation unit derives a mergingcandidate including a motion vector which is a zero vector to areferable reference picture, and newly registers the derived mergingcandidate in a merging candidate list. The merging candidate derived inthis manner is reliable when the current block is a stationary region,and coding efficiency therefore increases.

Note that the picture coding apparatus is not limited to the exampledescribed in Embodiment 5, in which a derived merging candidate includesa motion vector for a stationary region which is a zero vector. Forexample, a derived merging candidate may include a motion vector havinga value slightly larger or smaller than a zero vector (0, 0) (forexample, a motion vector (0, 1)) with consideration for small camerashake during video shooting. Optionally, a derived merging candidate mayhave a motion vector (OffsetX, OffsetY) which is provided by adding anoffset parameter (OffsetX, OffsetY) to a header or the like of asequence, a picture, or a slice.

Embodiment 6

In Embodiment 6, a process for deriving a combined merging candidatewill be described in detail using a drawing. The process for deriving acombined merging candidate described herein is an example of the firstderivation process or the second derivation process.

FIG. 21 is a flowchart showing the process for deriving a combinedmerging candidate according to Embodiment 6. Specifically, FIG. 21 showspart of processing operations of the merging candidate derivation unit110, 210, 314, or 411 in Embodiments 1 to 4. In other words, FIG. 21shows processing operations of the first derivation unit or the secondderivation unit.

In Step S601, the merging candidate derivation unit updates mergingcandidate indices idx1 and idx2. The merging candidate indices idx1 andidx2 are indices for determining two merging candidates to be used forderiving a combined merging candidate.

For example, the merging candidate derivation unit updates mergingcandidate indices idx1 and idx2 to “0” and “1”, respectively. In thiscase, the merging candidate derivation unit performs Steps S602 to S610described below to derive a combined merging candidate by combining aset of a prediction direction, a motion vector, and a reference pictureindex included in a merging candidate [0] and a set of a predictiondirection, a motion vector, and a reference picture index included in amerging candidate [1]. The merging candidate [0] is a merging candidateprovided with a merging candidate index having a value of 0 in a mergingcandidate list, and the merging candidate [1] is a merging candidateprovided with a merging candidate index having a value of 1 in themerging candidate list. The merging candidate derivation unit updatesmerging candidate indices idx1 and idx2 in Step S601 for each cycle ofderivation of a combined merging candidate. Note that details of theprocess for updating the merging candidate indices idx1 and idx2 is notlimited to a specific procedure. Any procedure is applicable throughwhich a combined merging candidate is derived using any combination ofmerging candidates derived before the derivation of the combined mergingcandidate.

In Step S602, the merging candidate derivation unit determines whetherit is true or false that (1) the values of the merging candidate indicesidx1 and idx2 are not identical, (2) a merging candidate [idx1] is not acombined merging candidate, and (3) a merging candidate [idx2] is not acombined merging candidate.

When the result of the determination in Step S602 is true (S142, Yes),the merging candidate derivation unit determines in Step S603 whether atleast one of the following is true: (1) the prediction directions of themerging candidate [idx1] and the merging candidate [idx2] are different;and (2) both the merging candidate [idx1] and the merging candidate[idx2] are bi-predictive. When the result of the determination in StepS603 is true, (S603, Yes), the merging candidate derivation unitdetermines in Step S604 whether both of the following are true: (1) themerging candidate [idx1] is a merging candidate for the predictiondirection 0 or bi-predictive; and (2) the merging candidate [idx2] is amerging candidate for the prediction direction 1 or bi-predictive. Inother words, the merging candidate derivation unit determines whether itis true or false that the merging candidate [idx1] includes at least amotion vector having the prediction direction 0, and the mergingcandidate [idx2] includes at least a motion vector having the predictiondirection 1.

When the result of the determination in Step S604 is true (S604, Yes),the merging candidate derivation unit in Step S605 assigns the motionvector and reference picture index for the prediction direction 0 whichare included in the merging candidate [idx1] to the motion vector andreference picture index for the prediction direction 0 of the combinedmerging candidate. Moreover, in Step S606, the merging candidatederivation unit assigns the motion vector and reference picture indexfor the prediction direction 1 which are included in the mergingcandidate [idx2] to the motion vector and reference picture index forthe prediction direction 1 of the combined merging candidate. Themerging candidate derivation unit thereby derives a bi-predictivecombined merging candidate.

When the result of the determination in Step S604 is false (S604, No),the merging candidate derivation unit in Step S607 assigns the motionvector and reference picture index for the prediction direction 0 whichare included in the merging candidate [idx2] to the motion vector andreference picture index for the prediction direction 0 of the combinedmerging candidate. Moreover, in Step S608, the merging candidatederivation unit assigns the motion vector and reference picture indexfor the prediction direction 1 which are included in the mergingcandidate [idx1] to the motion vector and reference picture index forthe prediction direction 1 of the combined merging candidate. Themerging candidate derivation unit thereby derives a bi-predictivecombined merging candidate.

In Step S609, the merging candidate derivation unit determines whetheror not the merging candidate list already includes a merging candidatewhich is identical in prediction direction, motion vector, and referencepicture index to the derived combined merging candidate. In other words,the merging candidate derivation unit determines whether or not thederived combined merging candidate is an identical candidate.

When the result of Step S609 is false (S609, No), the merging candidatederivation unit registers the derived combined merging candidate in themerging candidate list in Step S610.

When the result of the determination in Step S602 or Step S603 is false(S602 or S603, No), the merging candidate derivation unit does notregister the derived combined merging candidate in the merging candidatelist.

In this manner, the merging candidate derivation unit derives a combinedmerging candidate and registers the derived combined merging candidatein a merging candidate list.

Note that the picture coding apparatus is not limited to the exampledescribed in Embodiment 6, in which the merging candidate derivationunit determines in Step S609 whether or not a combined merging candidateis an identical candidate. For example, the merging candidate derivationunit may skip the determination in Step S609. This reduces computationalcomplexity in deriving a merging candidate for the merging candidatederivation unit.

In this manner, the merging candidate derivation unit according toEmbodiment 6 derives a bi-predictive merging candidate by making acombination from previously derived merging candidates. The mergingcandidate derivation unit is thus capable of deriving a newbi-predictive first merging candidate even when previously derivedmerging candidates include no bi-predictive merging candidate. As aresult, the merging candidate derivation unit increases the variety ofmerging candidates, and coding efficiency thereby increases.

Embodiment 7

In Embodiment 7, a process for deriving a scaling merging candidate willbe described in detail using drawings. The process for deriving ascaling merging candidate described herein is an example of the firstderivation process or the second derivation process.

FIG. 22 is a flowchart showing the process for deriving a scalingmerging candidate according to Embodiment 7. Specifically, FIG. 22 showspart of processing operations of the merging candidate derivation unit110, 210, 314, or 411 in Embodiments 1 to 4. In other words, FIG. 22shows processing operations of the first derivation unit or the secondderivation unit.

In Step S701, the merging candidate derivation unit updates a predictiondirection index X. In Step S702, the merging candidate derivation unitupdates a merging candidate index idx. The prediction direction index Xand the merging candidate index idx are indices for determination of aprediction direction and a merging candidate which are used for derivinga scaling merging candidate.

For example, the merging candidate derivation unit updates theprediction direction index X to “0” and the merging candidate index idxto “0”. In this case, the merging candidate derivation unit performsSteps S702 to S711 described below to derive a scaling merging candidateusing a motion vector and a reference picture index for a predictiondirection 0 included in a merging candidate [0], which is provided witha merging candidate index of 0 in a merging candidate list. The mergingcandidate derivation unit updates the prediction direction X in StepS701 and the merging candidate index idx in Step S702 for each cycle ofderivation of a scaling merging candidate.

In Step S703, the merging candidate derivation unit determines whetherit is true or false that (i) the merging candidate [idx] is not ascaling merging candidate and (ii) the merging candidate [idx] includesa motion vector having a prediction direction X. When the result of thedetermination in Step S703 is true (S703, Yes), the merging candidatederivation unit in Step S704 calculates a motion vector mvL(1−X) and areference picture index refIdxL(1−X) for a prediction direction (1−X)using the motion vector mvLX and reference picture index refIdxLX forthe prediction direction X which are included in the merging candidate[idx]. For example, the merging candidate derivation unit calculates themvL(1−X) and refIdxL(1−X) using Equations 2 and 3 shown below.refIdxL(1−X)=refIdxLX  (Equation 3)mvL(1−X)=mvLX×(POC(refIdxL(1−X))−curPOC)/(POC(refIdxLX)−curPOC)  (Equation 4)

POC (refIdxLX) denotes the display order of a reference pictureindicated by a reference picture index refIdxLX. POC (refIdxLX (1−X))denotes the display order of a reference picture indicated by areference picture index refIdxLX (1−X). curPOC denotes the display orderof a current picture to be coded.

FIG. 23 shows an example of a motion vector and a reference pictureindex calculated in Embodiment 7. As shown in FIG. 23 , the mergingcandidate derivation unit performs scaling using a motion vector mvLXand a reference picture index refIdxLX, which are a motion vector and areference picture index for one prediction direction (predictiondirection X) and included in a merging candidate, to calculate a motionvector mvL(1−X) and a reference picture index refIdxL(1−X), which are amotion vector and a reference picture index for the other predictiondirection (a prediction direction (1−X)).

In Step S705, the merging candidate derivation unit determines whetheror not the value of the prediction direction index X is “0”. When theresult of the determination in Step S705 is true (S705, Yes), themerging candidate derivation unit in Step S706 assigns the motion vectorand reference picture index for the prediction direction 0 which areincluded in the merging candidate [idx1] to the motion vector andreference picture index for the prediction direction 0 of the scalingmerging candidate. Moreover, in Step S707, the merging candidatederivation unit assigns the calculated motion vector mvL(1−X) andreference picture index refIdxL1(1−X) for the prediction direction (1−X)to the motion vector and reference picture index for the predictiondirection 1 of the scaling merging candidate. The merging candidatederivation unit thereby derives a bi-predictive scaling mergingcandidate.

When the result of the determination in Step S705 is false (that is,when the value of the prediction direction X is “1”) (S705, No), themerging candidate derivation unit in Step S708 assigns the calculatedmotion vector mvL(1−X) and reference picture index refIdxL1(1−X) for theprediction direction (1−X) to the motion vector and reference pictureindex for the prediction direction 0 of the scaling merging candidate.Moreover, in Step S709, the merging candidate derivation unit assignsthe motion vector and reference picture index for the predictiondirection X which are included in the merging candidate [idx] to themotion vector and reference picture index for the prediction direction 1of the scaling merging candidate. The merging candidate derivation unitthereby derives a bi-predictive scaling merging candidate.

In Step S710, the merging candidate derivation unit determines whetheror not the merging candidate list already includes a merging candidatewhich is identical in prediction direction, motion vector, and referencepicture index to the derived scaling merging candidate. In other words,the merging candidate derivation unit determines whether or not thederived scaling merging candidate is an identical candidate.

When the result of Step S710 is false (S710, No), the merging candidatederivation unit registers the derived scaling merging candidate in themerging candidate list in Step S711.

When the result of the determination in Step S703 is false (S703, No),or when the result of the determination in Step S710 is true (S710,Yes), the merging candidate derivation unit does not register thederived scaling merging candidate in the merging candidate list.

In this manner, the merging candidate derivation unit derives a scalingmerging candidate and registers the derived scaling merging candidate ina merging candidate list.

Note that the merging candidate derivation unit need not add a derivedscaling merging candidate to a merging candidate list when POC(refIdxLX) and POC (refIdxL(1−X)) are identical (that is, refIdxLX andrefIdxL(1−X) indicates the same picture), and thus providing mvL(1−X)and mvLX having the same values. Also note that when the value of acalculated refIdxL(1−X) is not included in a reference picture listL(1−X), the merging candidate derivation unit need not register ascaling merging candidate in a merging candidate list.

Optionally, the merging candidate derivation unit may calculate mvL(1−X)by directly assigning−mvLX to mvL(1−X) only when a condition that thevalues of POC (refIdxLX) and POC (refIdxL(1−X)) are different and acondition that the absolute values of (POC (refIdxL(1−X))−curPOC) and(POC (refIdxLX)−curPOC) are equal are both satisfied. The formercondition is satisfied when the picture indicated by refIdxLX and thepicture indicated by refIdxL(1−X) are different. The latter condition issatisfied when the picture indicated by refIdxLX and the pictureindicated by refIdxL(1−X) are equidistant in display order from thecurrent picture. When both are satisfied, mvL(1−X) is the inverse vectorof mvLX. When this is the case, the merging candidate derivation unitcan derive a scaling merging candidate without performing the scalingrepresented by Equation 4. Coding efficiency thereby increases with asmall increase in computational complexity.

Note that the picture coding apparatus is not limited to the exampledescribed in Embodiment 7, in which the merging candidate derivationunit determines in Step S710 whether or not a scaling merging candidateis an identical candidate. For example, the merging candidate derivationunit may skip the determination in Step S710. This reduces computationalcomplexity in deriving a merging candidate for the merging candidatederivation unit.

Although the picture coding apparatus and picture decoding apparatusaccording to one or more aspects of the present disclosure have beendescribed using exemplary embodiments, the present invention is notlimited to the exemplary embodiments. Those skilled in the art willreadily appreciate that many modifications of the exemplary embodimentsor embodiments in which the constituent elements of the exemplaryembodiments are combined are possible without materially departing fromthe novel teachings and advantages described in the present disclosure.All such modifications and embodiments are also within scopes of the oneor more aspects.

In the exemplary embodiments, each of the constituent elements may beimplemented as a piece of dedicated hardware or implemented by executinga software program appropriate for the constituent element. Theconstituent elements may be implemented by a program execution unit suchas a CPU or a processor which reads and executes a software programrecorded on a recording medium such as a hard disk or a semiconductormemory. Here, examples of the software program which implements thepicture coding apparatus or the picture decoding apparatus in theembodiments include a program as follows.

One is a program which causes a computer to execute a picture codingmethod for coding a picture on a block-by-block basis to generate abitstream, and the method includes: performing a first derivationprocess for deriving a first merging candidate which includes acandidate set of a prediction direction, a motion vector, and areference picture index for use in coding of a current block; performinga second derivation process for deriving a second merging candidatewhich includes a candidate set of a prediction direction, a motionvector, and a reference picture index for use in the coding of thecurrent block, the second derivation process being different from thefirst derivation process; selecting a merging candidate to be used inthe coding of the current block from among the first merging candidateand the second merging candidate; and attaching an index for identifyingthe selected merging candidate to the bitstream, wherein in theperforming of a first derivation process, the first derivation processis performed so that a total number of the first merging candidates doesnot exceed a predetermined number, and the second derivation process isperformed when the total number of the first merging candidates is lessthan a predetermined maximum number of merging candidates.

Another is a program which causes a computer to execute a picturedecoding method for decoding, on a block-by-block basis, a coded imageincluded in a bitstream, and the method includes: performing a firstderivation process for deriving a first merging candidate which includesa candidate set of a prediction direction, a motion vector, and areference picture index for use in decoding of a current block;performing a second derivation process for deriving a second mergingcandidate which includes a candidate set of a prediction direction, amotion vector, and a reference picture index for use in the decoding ofthe current block, the second derivation process being different fromthe first derivation process; obtaining an index from the bitstream; andselecting, based on the obtained index, a merging candidate to be usedin the decoding of the current block from among the first mergingcandidate and the second merging candidate, wherein in the performing ofa first derivation process, the first derivation process is performed sothat a total number of the first merging candidates does not exceed apredetermined number, and the second derivation process is performedwhen the total number of the first merging candidates is less than apredetermined maximum number of merging candidates.

Embodiment 8

The processing described in each of embodiments can be simplyimplemented in an independent computer system, by recording, in arecording medium, a program for implementing the configurations of themoving picture coding method (image coding method) and the movingpicture decoding method (image decoding method) described in each ofembodiments. The recording media may be any recording media as long asthe program can be recorded, such as a magnetic disk, an optical disk, amagnetic optical disk, an IC card, and a semiconductor memory.

Hereinafter, the applications to the moving picture coding method (imagecoding method) and the moving picture decoding method (image decodingmethod) described in each of embodiments and systems using thereof willbe described. The system has a feature of having an image coding anddecoding apparatus that includes an image coding apparatus using theimage coding method and an image decoding apparatus using the imagedecoding method. Other configurations in the system can be changed asappropriate depending on the cases.

FIG. 24 illustrates an overall configuration of a content providingsystem ex100 for implementing content distribution services. The areafor providing communication services is divided into cells of desiredsize, and base stations ex106, ex107, ex108, ex109, and ex110 which arefixed wireless stations are placed in each of the cells.

The content providing system ex100 is connected to devices, such as acomputer ex111, a personal digital assistant (PDA) ex112, a cameraex113, a cellular phone ex114 and a game machine ex115, via the Internetex101, an Internet service provider ex102, a telephone network ex104, aswell as the base stations ex106 to ex110, respectively.

However, the configuration of the content providing system ex100 is notlimited to the configuration shown in FIG. 24 , and a combination inwhich any of the elements are connected is acceptable. In addition, eachdevice may be directly connected to the telephone network ex104, ratherthan via the base stations ex106 to ex110 which are the fixed wirelessstations. Furthermore, the devices may be interconnected to each othervia a short distance wireless communication and others.

The camera ex113, such as a digital video camera, is capable ofcapturing video. A camera ex116, such as a digital camera, is capable ofcapturing both still images and video. Furthermore, the cellular phoneex114 may be the one that meets any of the standards such as GlobalSystem for Mobile Communications (GSM) (registered trademark), CodeDivision Multiple Access (CDMA), Wideband-Code Division Multiple Access(W-CDMA), Long Term Evolution (LTE), and High Speed Packet Access(HSPA). Alternatively, the cellular phone ex114 may be a PersonalHandyphone System (PHS).

In the content providing system ex100, a streaming server ex103 isconnected to the camera ex113 and others via the telephone network ex104and the base station ex109, which enables distribution of images of alive show and others. In such a distribution, a content (for example,video of a music live show) captured by the user using the camera ex113is coded as described above in each of embodiments (i.e., the camerafunctions as the image coding apparatus according to an aspect of thepresent disclosure), and the coded content is transmitted to thestreaming server ex103. On the other hand, the streaming server ex103carries out stream distribution of the transmitted content data to theclients upon their requests. The clients include the computer ex111, thePDA ex112, the camera ex113, the cellular phone ex114, and the gamemachine ex115 that are capable of decoding the above-mentioned codeddata. Each of the devices that have received the distributed datadecodes and reproduces the coded data (i.e., functions as the imagedecoding apparatus according to an aspect of the present disclosure).

The captured data may be coded by the camera ex113 or the streamingserver ex103 that transmits the data, or the coding processes may beshared between the camera ex113 and the streaming server ex103.Similarly, the distributed data may be decoded by the clients or thestreaming server ex103, or the decoding processes may be shared betweenthe clients and the streaming server ex103. Furthermore, the data of thestill images and video captured by not only the camera ex113 but alsothe camera ex116 may be transmitted to the streaming server ex103through the computer ex111. The coding processes may be performed by thecamera ex116, the computer ex111, or the streaming server ex103, orshared among them.

Furthermore, the coding and decoding processes may be performed by anLSI ex500 generally included in each of the computer ex111 and thedevices. The LSI ex500 may be configured of a single chip or a pluralityof chips. Software for coding and decoding video may be integrated intosome type of a recording medium (such as a CD-ROM, a flexible disk, anda hard disk) that is readable by the computer ex111 and others, and thecoding and decoding processes may be performed using the software.Furthermore, when the cellular phone ex114 is equipped with a camera,the video data obtained by the camera may be transmitted. The video datais data coded by the LSI ex500 included in the cellular phone ex114.

Furthermore, the streaming server ex103 may be composed of servers andcomputers, and may decentralize data and process the decentralized data,record, or distribute data.

As described above, the clients may receive and reproduce the coded datain the content providing system ex100. In other words, the clients canreceive and decode information transmitted by the user, and reproducethe decoded data in real time in the content providing system ex100, sothat the user who does not have any particular right and equipment canimplement personal broadcasting.

Aside from the example of the content providing system ex100, at leastone of the moving picture coding apparatus (image coding apparatus) andthe moving picture decoding apparatus (image decoding apparatus)described in each of embodiments may be implemented in a digitalbroadcasting system ex200 illustrated in FIG. 25 . More specifically, abroadcast station ex201 communicates or transmits, via radio waves to abroadcast satellite ex202, multiplexed data obtained by multiplexingaudio data and others onto video data. The video data is data coded bythe moving picture coding method described in each of embodiments (i.e.,data coded by the image coding apparatus according to an aspect of thepresent disclosure). Upon receipt of the multiplexed data, the broadcastsatellite ex202 transmits radio waves for broadcasting. Then, a home-useantenna ex204 with a satellite broadcast reception function receives theradio waves. Next, a device such as a television (receiver) ex300 and aset top box (STB) ex217 decodes the received multiplexed data, andreproduces the decoded data (i.e., functions as the image decodingapparatus according to an aspect of the present disclosure).

Furthermore, a reader/recorder ex218 (i) reads and decodes themultiplexed data recorded on a recording medium ex215, such as a DVD anda BD, or (i) codes video signals in the recording medium ex215, and insome cases, writes data obtained by multiplexing an audio signal on thecoded data. The reader/recorder ex218 can include the moving picturedecoding apparatus or the moving picture coding apparatus as shown ineach of embodiments. In this case, the reproduced video signals aredisplayed on the monitor ex219, and can be reproduced by another deviceor system using the recording medium ex215 on which the multiplexed datais recorded. It is also possible to implement the moving picturedecoding apparatus in the set top box ex217 connected to the cable ex203for a cable television or to the antenna ex204 for satellite and/orterrestrial broadcasting, so as to display the video signals on themonitor ex219 of the television ex300. The moving picture decodingapparatus may be implemented not in the set top box but in thetelevision ex300.

FIG. 26 illustrates the television (receiver) ex300 that uses the movingpicture coding method and the moving picture decoding method describedin each of embodiments. The television ex300 includes: a tuner ex301that obtains or provides multiplexed data obtained by multiplexing audiodata onto video data, through the antenna ex204 or the cable ex203, etc.that receives a broadcast; a modulation/demodulation unit ex302 thatdemodulates the received multiplexed data or modulates data intomultiplexed data to be supplied outside; and amultiplexing/demultiplexing unit ex303 that demultiplexes the modulatedmultiplexed data into video data and audio data, or multiplexes videodata and audio data coded by a signal processing unit ex306 into data.

The television ex300 further includes: a signal processing unit ex306including an audio signal processing unit ex304 and a video signalprocessing unit ex305 that decode audio data and video data and codeaudio data and video data, respectively (which function as the imagecoding apparatus and the image decoding apparatus according to theaspects of the present disclosure); and an output unit ex309 including aspeaker ex307 that provides the decoded audio signal, and a display unitex308 that displays the decoded video signal, such as a display.Furthermore, the television ex300 includes an interface unit ex317including an operation input unit ex312 that receives an input of a useroperation. Furthermore, the television ex300 includes a control unitex310 that controls overall each constituent element of the televisionex300, and a power supply circuit unit ex311 that supplies power to eachof the elements. Other than the operation input unit ex312, theinterface unit ex317 may include: a bridge ex313 that is connected to anexternal device, such as the reader/recorder ex218; a slot unit ex314for enabling attachment of the recording medium ex216, such as an SDcard; a driver ex315 to be connected to an external recording medium,such as a hard disk; and a modem ex316 to be connected to a telephonenetwork. Here, the recording medium ex216 can electrically recordinformation using a non-volatile/volatile semiconductor memory elementfor storage. The constituent elements of the television ex300 areconnected to each other through a synchronous bus.

First, the configuration in which the television ex300 decodesmultiplexed data obtained from outside through the antenna ex204 andothers and reproduces the decoded data will be described. In thetelevision ex300, upon a user operation through a remote controllerex220 and others, the multiplexing/demultiplexing unit ex303demultiplexes the multiplexed data demodulated by themodulation/demodulation unit ex302, under control of the control unitex310 including a CPU. Furthermore, the audio signal processing unitex304 decodes the demultiplexed audio data, and the video signalprocessing unit ex305 decodes the demultiplexed video data, using thedecoding method described in each of embodiments, in the televisionex300. The output unit ex309 provides the decoded video signal and audiosignal outside, respectively. When the output unit ex309 provides thevideo signal and the audio signal, the signals may be temporarily storedin buffers ex318 and ex319, and others so that the signals arereproduced in synchronization with each other. Furthermore, thetelevision ex300 may read multiplexed data not through a broadcast andothers but from the recording media ex215 and ex216, such as a magneticdisk, an optical disk, and a SD card. Next, a configuration in which thetelevision ex300 codes an audio signal and a video signal, and transmitsthe data outside or writes the data on a recording medium will bedescribed. In the television ex300, upon a user operation through theremote controller ex220 and others, the audio signal processing unitex304 codes an audio signal, and the video signal processing unit ex305codes a video signal, under control of the control unit ex310 using thecoding method described in each of embodiments. Themultiplexing/demultiplexing unit ex303 multiplexes the coded videosignal and audio signal, and provides the resulting signal outside. Whenthe multiplexing/demultiplexing unit ex303 multiplexes the video signaland the audio signal, the signals may be temporarily stored in thebuffers ex320 and ex321, and others so that the signals are reproducedin synchronization with each other. Here, the buffers ex318, ex319,ex320, and ex321 may be plural as illustrated, or at least one buffermay be shared in the television ex300. Furthermore, data may be storedin a buffer so that the system overflow and underflow may be avoidedbetween the modulation/demodulation unit ex302 and themultiplexing/demultiplexing unit ex303, for example.

Furthermore, the television ex300 may include a configuration forreceiving an AV input from a microphone or a camera other than theconfiguration for obtaining audio and video data from a broadcast or arecording medium, and may code the obtained data. Although thetelevision ex300 can code, multiplex, and provide outside data in thedescription, it may be capable of only receiving, decoding, andproviding outside data but not the coding, multiplexing, and providingoutside data.

Furthermore, when the reader/recorder ex218 reads or writes multiplexeddata from or on a recording medium, one of the television ex300 and thereader/recorder ex218 may decode or code the multiplexed data, and thetelevision ex300 and the reader/recorder ex218 may share the decoding orcoding.

As an example, FIG. 27 illustrates a configuration of an informationreproducing/recording unit ex400 when data is read or written from or onan optical disk. The information reproducing/recording unit ex400includes constituent elements ex401, ex402, ex403, ex404, ex405, ex406,and ex407 to be described hereinafter. The optical head ex401 irradiatesa laser spot in a recording surface of the recording medium ex215 thatis an optical disk to write information, and detects reflected lightfrom the recording surface of the recording medium ex215 to read theinformation. The modulation recording unit ex402 electrically drives asemiconductor laser included in the optical head ex401, and modulatesthe laser light according to recorded data. The reproductiondemodulating unit ex403 amplifies a reproduction signal obtained byelectrically detecting the reflected light from the recording surfaceusing a photo detector included in the optical head ex401, anddemodulates the reproduction signal by separating a signal componentrecorded on the recording medium ex215 to reproduce the necessaryinformation. The buffer ex404 temporarily holds the information to berecorded on the recording medium ex215 and the information reproducedfrom the recording medium ex215. The disk motor ex405 rotates therecording medium ex215. The servo control unit ex406 moves the opticalhead ex401 to a predetermined information track while controlling therotation drive of the disk motor ex405 so as to follow the laser spot.The system control unit ex407 controls overall the informationreproducing/recording unit ex400. The reading and writing processes canbe implemented by the system control unit ex407 using variousinformation stored in the buffer ex404 and generating and adding newinformation as necessary, and by the modulation recording unit ex402,the reproduction demodulating unit ex403, and the servo control unitex406 that record and reproduce information through the optical headex401 while being operated in a coordinated manner. The system controlunit ex407 includes, for example, a microprocessor, and executesprocessing by causing a computer to execute a program for read andwrite.

Although the optical head ex401 irradiates a laser spot in thedescription, it may perform high-density recording using near fieldlight.

FIG. 28 illustrates the recording medium ex215 that is the optical disk.On the recording surface of the recording medium ex215, guide groovesare spirally formed, and an information track ex230 records, in advance,address information indicating an absolute position on the diskaccording to change in a shape of the guide grooves. The addressinformation includes information for determining positions of recordingblocks ex231 that are a unit for recording data. Reproducing theinformation track ex230 and reading the address information in anapparatus that records and reproduces data can lead to determination ofthe positions of the recording blocks. Furthermore, the recording mediumex215 includes a data recording area ex233, an inner circumference areaex232, and an outer circumference area ex234. The data recording areaex233 is an area for use in recording the user data. The innercircumference area ex232 and the outer circumference area ex234 that areinside and outside of the data recording area ex233, respectively arefor specific use except for recording the user data. The informationreproducing/recording unit 400 reads and writes coded audio, coded videodata, or multiplexed data obtained by multiplexing the coded audio andvideo data, from and on the data recording area ex233 of the recordingmedium ex215.

Although an optical disk having a layer, such as a DVD and a BD isdescribed as an example in the description, the optical disk is notlimited to such, and may be an optical disk having a multilayerstructure and capable of being recorded on a part other than thesurface. Furthermore, the optical disk may have a structure formultidimensional recording/reproduction, such as recording ofinformation using light of colors with different wavelengths in the sameportion of the optical disk and for recording information havingdifferent layers from various angles.

Furthermore, a car ex210 having an antenna ex205 can receive data fromthe satellite ex202 and others, and reproduce video on a display devicesuch as a car navigation system ex211 set in the car ex210, in thedigital broadcasting system ex200. Here, a configuration of the carnavigation system ex211 will be a configuration, for example, includinga GPS receiving unit from the configuration illustrated in FIG. 26 . Thesame will be true for the configuration of the computer ex111, thecellular phone ex114, and others.

FIG. 29A illustrates the cellular phone ex114 that uses the movingpicture coding method and the moving picture decoding method describedin embodiments. The cellular phone ex114 includes: an antenna ex350 fortransmitting and receiving radio waves through the base station ex110; acamera unit ex365 capable of capturing moving and still images; and adisplay unit ex358 such as a liquid crystal display for displaying thedata such as decoded video captured by the camera unit ex365 or receivedby the antenna ex350. The cellular phone ex114 further includes: a mainbody unit including an operation key unit ex366; an audio output unitex357 such as a speaker for output of audio; an audio input unit ex356such as a microphone for input of audio; a memory unit ex367 for storingcaptured video or still pictures, recorded audio, coded or decoded dataof the received video, the still pictures, e-mails, or others; and aslot unit ex364 that is an interface unit for a recording medium thatstores data in the same manner as the memory unit ex367.

Next, an example of a configuration of the cellular phone ex114 will bedescribed with reference to FIG. 29B. In the cellular phone ex114, amain control unit ex360 designed to control overall each unit of themain body including the display unit ex358 as well as the operation keyunit ex366 is connected mutually, via a synchronous bus ex370, to apower supply circuit unit ex361, an operation input control unit ex362,a video signal processing unit ex355, a camera interface unit ex363, aliquid crystal display (LCD) control unit ex359, amodulation/demodulation unit ex352, a multiplexing/demultiplexing unitex353, an audio signal processing unit ex354, the slot unit ex364, andthe memory unit ex367.

When a call-end key or a power key is turned ON by a user's operation,the power supply circuit unit ex361 supplies the respective units withpower from a battery pack so as to activate the cell phone ex114.

In the cellular phone ex114, the audio signal processing unit ex354converts the audio signals collected by the audio input unit ex356 invoice conversation mode into digital audio signals under the control ofthe main control unit ex360 including a CPU, ROM, and RAM. Then, themodulation/demodulation unit ex352 performs spread spectrum processingon the digital audio signals, and the transmitting and receiving unitex351 performs digital-to-analog conversion and frequency conversion onthe data, so as to transmit the resulting data via the antenna ex350.Also, in the cellular phone ex114, the transmitting and receiving unitex351 amplifies the data received by the antenna ex350 in voiceconversation mode and performs frequency conversion and theanalog-to-digital conversion on the data. Then, themodulation/demodulation unit ex352 performs inverse spread spectrumprocessing on the data, and the audio signal processing unit ex354converts it into analog audio signals, so as to output them via theaudio output unit ex357.

Furthermore, when an e-mail in data communication mode is transmitted,text data of the e-mail inputted by operating the operation key unitex366 and others of the main body is sent out to the main control unitex360 via the operation input control unit ex362. The main control unitex360 causes the modulation/demodulation unit ex352 to perform spreadspectrum processing on the text data, and the transmitting and receivingunit ex351 performs the digital-to-analog conversion and the frequencyconversion on the resulting data to transmit the data to the basestation ex110 via the antenna ex350. When an e-mail is received,processing that is approximately inverse to the processing fortransmitting an e-mail is performed on the received data, and theresulting data is provided to the display unit ex358.

When video, still images, or video and audio in data communication modeis or are transmitted, the video signal processing unit ex355 compressesand codes video signals supplied from the camera unit ex365 using themoving picture coding method shown in each of embodiments (i.e.,functions as the image coding apparatus according to the aspect of thepresent disclosure), and transmits the coded video data to themultiplexing/demultiplexing unit ex353. In contrast, during when thecamera unit ex365 captures video, still images, and others, the audiosignal processing unit ex354 codes audio signals collected by the audioinput unit ex356, and transmits the coded audio data to themultiplexing/demultiplexing unit ex353.

The multiplexing/demultiplexing unit ex353 multiplexes the coded videodata supplied from the video signal processing unit ex355 and the codedaudio data supplied from the audio signal processing unit ex354, using apredetermined method. Then, the modulation/demodulation unit(modulation/demodulation circuit unit) ex352 performs spread spectrumprocessing on the multiplexed data, and the transmitting and receivingunit ex351 performs digital-to-analog conversion and frequencyconversion on the data so as to transmit the resulting data via theantenna ex350.

When receiving data of a video file which is linked to a Web page andothers in data communication mode or when receiving an e-mail with videoand/or audio attached, in order to decode the multiplexed data receivedvia the antenna ex350, the multiplexing/demultiplexing unit ex353demultiplexes the multiplexed data into a video data bit stream and anaudio data bit stream, and supplies the video signal processing unitex355 with the coded video data and the audio signal processing unitex354 with the coded audio data, through the synchronous bus ex370. Thevideo signal processing unit ex355 decodes the video signal using amoving picture decoding method corresponding to the moving picturecoding method shown in each of embodiments (i.e., functions as the imagedecoding apparatus according to the aspect of the present disclosure),and then the display unit ex358 displays, for instance, the video andstill images included in the video file linked to the Web page via theLCD control unit ex359. Furthermore, the audio signal processing unitex354 decodes the audio signal, and the audio output unit ex357 providesthe audio.

Furthermore, similarly to the television ex300, a terminal such as thecellular phone ex114 probably have 3 types of implementationconfigurations including not only (i) a transmitting and receivingterminal including both a coding apparatus and a decoding apparatus, butalso (ii) a transmitting terminal including only a coding apparatus and(iii) a receiving terminal including only a decoding apparatus. Althoughthe digital broadcasting system ex200 receives and transmits themultiplexed data obtained by multiplexing audio data onto video data inthe description, the multiplexed data may be data obtained bymultiplexing not audio data but character data related to video ontovideo data, and may be not multiplexed data but video data itself.

As such, the moving picture coding method and the moving picturedecoding method in each of embodiments can be used in any of the devicesand systems described. Thus, the advantages described in each ofembodiments can be obtained.

Furthermore, various modifications and revisions can be made in any ofthe embodiments in the present disclosure.

Embodiment 9

Video data can be generated by switching, as necessary, between (i) themoving picture coding method or the moving picture coding apparatusshown in each of embodiments and (ii) a moving picture coding method ora moving picture coding apparatus in conformity with a differentstandard, such as MPEG-2, MPEG-4 AVC, and VC-1.

Here, when a plurality of video data that conforms to the differentstandards is generated and is then decoded, the decoding methods need tobe selected to conform to the different standards. However, since towhich standard each of the plurality of the video data to be decodedconforms cannot be detected, there is a problem that an appropriatedecoding method cannot be selected.

In order to solve the problem, multiplexed data obtained by multiplexingaudio data and others onto video data has a structure includingidentification information indicating to which standard the video dataconforms. The specific structure of the multiplexed data including thevideo data generated in the moving picture coding method and by themoving picture coding apparatus shown in each of embodiments will behereinafter described. The multiplexed data is a digital stream in theMPEG-2 Transport Stream format.

FIG. 30 illustrates a structure of the multiplexed data. As illustratedin FIG. 30 , the multiplexed data can be obtained by multiplexing atleast one of a video stream, an audio stream, a presentation graphicsstream (PG), and an interactive graphics stream. The video streamrepresents primary video and secondary video of a movie, the audiostream (IG) represents a primary audio part and a secondary audio partto be mixed with the primary audio part, and the presentation graphicsstream represents subtitles of the movie. Here, the primary video isnormal video to be displayed on a screen, and the secondary video isvideo to be displayed on a smaller window in the primary video.Furthermore, the interactive graphics stream represents an interactivescreen to be generated by arranging the GUI components on a screen. Thevideo stream is coded in the moving picture coding method or by themoving picture coding apparatus shown in each of embodiments, or in amoving picture coding method or by a moving picture coding apparatus inconformity with a conventional standard, such as MPEG-2, MPEG-4 AVC, andVC-1. The audio stream is coded in accordance with a standard, such asDolby-AC-3, Dolby Digital Plus, MLP, DTS, DTS-HD, and linear PCM.

Each stream included in the multiplexed data is identified by PID. Forexample, 0x1011 is allocated to the video stream to be used for video ofa movie, 0x1100 to 0x111F are allocated to the audio streams, 0x1200 to0x121F are allocated to the presentation graphics streams, 0x1400 to0x141F are allocated to the interactive graphics streams, 0x1B00 to0x1B1F are allocated to the video streams to be used for secondary videoof the movie, and 0x1A00 to 0x1A1F are allocated to the audio streams tobe used for the secondary audio to be mixed with the primary audio.

FIG. 31 schematically illustrates how data is multiplexed. First, avideo stream ex235 composed of video frames and an audio stream ex238composed of audio frames are transformed into a stream of PES packetsex236 and a stream of PES packets ex239, and further into TS packetsex237 and TS packets ex240, respectively. Similarly, data of apresentation graphics stream ex241 and data of an interactive graphicsstream ex244 are transformed into a stream of PES packets ex242 and astream of PES packets ex245, and further into TS packets ex243 and TSpackets ex246, respectively. These TS packets are multiplexed into astream to obtain multiplexed data ex247.

FIG. 32 illustrates how a video stream is stored in a stream of PESpackets in more detail. The first bar in FIG. 32 shows a video framestream in a video stream. The second bar shows the stream of PESpackets. As indicated by arrows denoted as yy1, yy2, yy3, and yy4 inFIG. 32 , the video stream is divided into pictures as I pictures, Bpictures, and P pictures each of which is a video presentation unit, andthe pictures are stored in a payload of each of the PES packets. Each ofthe PES packets has a PES header, and the PES header stores aPresentation Time-Stamp (PTS) indicating a display time of the picture,and a Decoding Time-Stamp (DTS) indicating a decoding time of thepicture.

FIG. 33 illustrates a format of TS packets to be finally written on themultiplexed data. Each of the TS packets is a 188-byte fixed lengthpacket including a 4-byte TS header having information, such as a PIDfor identifying a stream and a 184-byte TS payload for storing data. ThePES packets are divided, and stored in the TS payloads, respectively.When a BD ROM is used, each of the TS packets is given a 4-byteTP_Extra_Header, thus resulting in 192-byte source packets. The sourcepackets are written on the multiplexed data. The TP_Extra_Header storesinformation such as an Arrival_Time_Stamp (ATS). The ATS shows atransfer start time at which each of the TS packets is to be transferredto a PID filter. The source packets are arranged in the multiplexed dataas shown at the bottom of FIG. 33 . The numbers incrementing from thehead of the multiplexed data are called source packet numbers (SPNs).

Each of the TS packets included in the multiplexed data includes notonly streams of audio, video, subtitles and others, but also a ProgramAssociation Table (PAT), a Program Map Table (PMT), and a Program ClockReference (PCR). The PAT shows what a PID in a PMT used in themultiplexed data indicates, and a PID of the PAT itself is registered aszero. The PMT stores PIDs of the streams of video, audio, subtitles andothers included in the multiplexed data, and attribute information ofthe streams corresponding to the PIDs. The PMT also has variousdescriptors relating to the multiplexed data. The descriptors haveinformation such as copy control information showing whether copying ofthe multiplexed data is permitted or not. The PCR stores STC timeinformation corresponding to an ATS showing when the PCR packet istransferred to a decoder, in order to achieve synchronization between anArrival Time Clock (ATC) that is a time axis of ATSs, and an System TimeClock (STC) that is a time axis of PTSs and DTSs.

FIG. 34 illustrates the data structure of the PMT in detail. A PMTheader is disposed at the top of the PMT. The PMT header describes thelength of data included in the PMT and others. A plurality ofdescriptors relating to the multiplexed data is disposed after the PMTheader. Information such as the copy control information is described inthe descriptors. After the descriptors, a plurality of pieces of streaminformation relating to the streams included in the multiplexed data isdisposed. Each piece of stream information includes stream descriptorseach describing information, such as a stream type for identifying acompression codec of a stream, a stream PID, and stream attributeinformation (such as a frame rate or an aspect ratio). The streamdescriptors are equal in number to the number of streams in themultiplexed data.

When the multiplexed data is recorded on a recording medium and others,it is recorded together with multiplexed data information files.

Each of the multiplexed data information files is management informationof the multiplexed data as shown in FIG. 35 . The multiplexed datainformation files are in one to one correspondence with the multiplexeddata, and each of the files includes multiplexed data information,stream attribute information, and an entry map.

As illustrated in FIG. 35 , the multiplexed data information includes asystem rate, a reproduction start time, and a reproduction end time. Thesystem rate indicates the maximum transfer rate at which a system targetdecoder to be described later transfers the multiplexed data to a PIDfilter. The intervals of the ATSs included in the multiplexed data areset to not higher than a system rate. The reproduction start timeindicates a PTS in a video frame at the head of the multiplexed data. Aninterval of one frame is added to a PTS in a video frame at the end ofthe multiplexed data, and the PTS is set to the reproduction end time.

As shown in FIG. 36 , a piece of attribute information is registered inthe stream attribute information, for each PID of each stream includedin the multiplexed data. Each piece of attribute information hasdifferent information depending on whether the corresponding stream is avideo stream, an audio stream, a presentation graphics stream, or aninteractive graphics stream. Each piece of video stream attributeinformation carries information including what kind of compression codecis used for compressing the video stream, and the resolution, aspectratio and frame rate of the pieces of picture data that is included inthe video stream. Each piece of audio stream attribute informationcarries information including what kind of compression codec is used forcompressing the audio stream, how many channels are included in theaudio stream, which language the audio stream supports, and how high thesampling frequency is. The video stream attribute information and theaudio stream attribute information are used for initialization of adecoder before the player plays back the information.

In the present embodiment, the multiplexed data to be used is of astream type included in the PMT. Furthermore, when the multiplexed datais recorded on a recording medium, the video stream attributeinformation included in the multiplexed data information is used. Morespecifically, the moving picture coding method or the moving picturecoding apparatus described in each of embodiments includes a step or aunit for allocating unique information indicating video data generatedby the moving picture coding method or the moving picture codingapparatus in each of embodiments, to the stream type included in the PMTor the video stream attribute information. With the configuration, thevideo data generated by the moving picture coding method or the movingpicture coding apparatus described in each of embodiments can bedistinguished from video data that conforms to another standard.

Furthermore, FIG. 37 illustrates steps of the moving picture decodingmethod according to the present embodiment. In Step exS100, the streamtype included in the PMT or the video stream attribute informationincluded in the multiplexed data information is obtained from themultiplexed data. Next, in Step exS101, it is determined whether or notthe stream type or the video stream attribute information indicates thatthe multiplexed data is generated by the moving picture coding method orthe moving picture coding apparatus in each of embodiments. When it isdetermined that the stream type or the video stream attributeinformation indicates that the multiplexed data is generated by themoving picture coding method or the moving picture coding apparatus ineach of embodiments, in Step exS102, decoding is performed by the movingpicture decoding method in each of embodiments. Furthermore, when thestream type or the video stream attribute information indicatesconformance to the conventional standards, such as MPEG-2, MPEG-4 AVC,and VC-1, in Step exS103, decoding is performed by a moving picturedecoding method in conformity with the conventional standards.

As such, allocating a new unique value to the stream type or the videostream attribute information enables determination whether or not themoving picture decoding method or the moving picture decoding apparatusthat is described in each of embodiments can perform decoding. Even whenmultiplexed data that conforms to a different standard is input, anappropriate decoding method or apparatus can be selected. Thus, itbecomes possible to decode information without any error. Furthermore,the moving picture coding method or apparatus, or the moving picturedecoding method or apparatus in the present embodiment can be used inthe devices and systems described above.

Embodiment 10

Each of the moving picture coding method, the moving picture codingapparatus, the moving picture decoding method, and the moving picturedecoding apparatus in each of embodiments is typically achieved in theform of an integrated circuit or a Large Scale Integrated (LSI) circuit.As an example of the LSI, FIG. 38 illustrates a configuration of the LSIex500 that is made into one chip. The LSI ex500 includes elements ex501,ex502, ex503, ex504, ex505, ex506, ex507, ex508, and ex509 to bedescribed below, and the elements are connected to each other through abus ex510. The power supply circuit unit ex505 is activated by supplyingeach of the elements with power when the power supply circuit unit ex505is turned on.

For example, when coding is performed, the LSI ex500 receives an AVsignal from a microphone ex117, a camera ex113, and others through an AVIO ex509 under control of a control unit ex501 including a CPU ex502, amemory controller ex503, a stream controller ex504, and a drivingfrequency control unit ex512. The received AV signal is temporarilystored in an external memory ex511, such as an SDRAM. Under control ofthe control unit ex501, the stored data is segmented into data portionsaccording to the processing amount and speed to be transmitted to asignal processing unit ex507. Then, the signal processing unit ex507codes an audio signal and/or a video signal. Here, the coding of thevideo signal is the coding described in each of embodiments.Furthermore, the signal processing unit ex507 sometimes multiplexes thecoded audio data and the coded video data, and a stream IO ex506provides the multiplexed data outside. The provided multiplexed data istransmitted to the base station ex107, or written on the recordingmedium ex215. When data sets are multiplexed, the data should betemporarily stored in the buffer ex508 so that the data sets aresynchronized with each other.

Although the memory ex511 is an element outside the LSI ex500, it may beincluded in the LSI ex500. The buffer ex508 is not limited to onebuffer, but may be composed of buffers. Furthermore, the LSI ex500 maybe made into one chip or a plurality of chips.

Furthermore, although the control unit ex501 includes the CPU ex502, thememory controller ex503, the stream controller ex504, the drivingfrequency control unit ex512, the configuration of the control unitex501 is not limited to such. For example, the signal processing unitex507 may further include a CPU. Inclusion of another CPU in the signalprocessing unit ex507 can improve the processing speed. Furthermore, asanother example, the CPU ex502 may serve as or be a part of the signalprocessing unit ex507, and, for example, may include an audio signalprocessing unit. In such a case, the control unit ex501 includes thesignal processing unit ex507 or the CPU ex502 including a part of thesignal processing unit ex507.

The name used here is LSI, but it may also be called IC, system LSI,super LSI, or ultra LSI depending on the degree of integration.

Moreover, ways to achieve integration are not limited to the LSI, and aspecial circuit or a general purpose processor and so forth can alsoachieve the integration. Field Programmable Gate Array (FPGA) that canbe programmed after manufacturing LSIs or a reconfigurable processorthat allows re-configuration of the connection or configuration of anLSI can be used for the same purpose.

In the future, with advancement in semiconductor technology, a brand-newtechnology may replace LSI. The functional blocks can be integratedusing such a technology. The possibility is that the present disclosureis applied to biotechnology.

Embodiment 11

When video data generated in the moving picture coding method or by themoving picture coding apparatus described in each of embodiments isdecoded, compared to when video data that conforms to a conventionalstandard, such as MPEG-2, MPEG-4 AVC, and VC-1 is decoded, theprocessing amount probably increases. Thus, the LSI ex500 needs to beset to a driving frequency higher than that of the CPU ex502 to be usedwhen video data in conformity with the conventional standard is decoded.However, when the driving frequency is set higher, there is a problemthat the power consumption increases.

In order to solve the problem, the moving picture decoding apparatus,such as the television ex300 and the LSI ex500 is configured todetermine to which standard the video data conforms, and switch betweenthe driving frequencies according to the determined standard. FIG. 39illustrates a configuration ex800 in the present embodiment. A drivingfrequency switching unit ex803 sets a driving frequency to a higherdriving frequency when video data is generated by the moving picturecoding method or the moving picture coding apparatus described in eachof embodiments. Then, the driving frequency switching unit ex803instructs a decoding processing unit ex801 that executes the movingpicture decoding method described in each of embodiments to decode thevideo data. When the video data conforms to the conventional standard,the driving frequency switching unit ex803 sets a driving frequency to alower driving frequency than that of the video data generated by themoving picture coding method or the moving picture coding apparatusdescribed in each of embodiments. Then, the driving frequency switchingunit ex803 instructs the decoding processing unit ex802 that conforms tothe conventional standard to decode the video data.

More specifically, the driving frequency switching unit ex803 includesthe CPU ex502 and the driving frequency control unit ex512 in FIG. 38 .Here, each of the decoding processing unit ex801 that executes themoving picture decoding method described in each of embodiments and thedecoding processing unit ex802 that conforms to the conventionalstandard corresponds to the signal processing unit ex507 in FIG. 38 .The CPU ex502 determines to which standard the video data conforms.Then, the driving frequency control unit ex512 determines a drivingfrequency based on a signal from the CPU ex502. Furthermore, the signalprocessing unit ex507 decodes the video data based on the signal fromthe CPU ex502. For example, the identification information described inEmbodiment B is probably used for identifying the video data. Theidentification information is not limited to the one described inEmbodiment B but may be any information as long as the informationindicates to which standard the video data conforms. For example, whenwhich standard video data conforms to can be determined based on anexternal signal for determining that the video data is used for atelevision or a disk, etc., the determination may be made based on suchan external signal. Furthermore, the CPU ex502 selects a drivingfrequency based on, for example, a look-up table in which the standardsof the video data are associated with the driving frequencies as shownin FIG. 41 . The driving frequency can be selected by storing thelook-up table in the buffer ex508 and in an internal memory of an LSI,and with reference to the look-up table by the CPU ex502.

FIG. 40 illustrates steps for executing a method in the presentembodiment. First, in Step exS200, the signal processing unit ex507obtains identification information from the multiplexed data. Next, inStep exS201, the CPU ex502 determines whether or not the video data isgenerated by the coding method and the coding apparatus described ineach of embodiments, based on the identification information. When thevideo data is generated by the moving picture coding method and themoving picture coding apparatus described in each of embodiments, inStep exS202, the CPU ex502 transmits a signal for setting the drivingfrequency to a higher driving frequency to the driving frequency controlunit ex512. Then, the driving frequency control unit ex512 sets thedriving frequency to the higher driving frequency. On the other hand,when the identification information indicates that the video dataconforms to the conventional standard, such as MPEG-2, MPEG-4 AVC, andVC-1, in Step exS203, the CPU ex502 transmits a signal for setting thedriving frequency to a lower driving frequency to the driving frequencycontrol unit ex512. Then, the driving frequency control unit ex512 setsthe driving frequency to the lower driving frequency than that in thecase where the video data is generated by the moving picture codingmethod and the moving picture coding apparatus described in each ofembodiment.

Furthermore, along with the switching of the driving frequencies, thepower conservation effect can be improved by changing the voltage to beapplied to the LSI ex500 or an apparatus including the LSI ex500. Forexample, when the driving frequency is set lower, the voltage to beapplied to the LSI ex500 or the apparatus including the LSI ex500 isprobably set to a voltage lower than that in the case where the drivingfrequency is set higher.

Furthermore, when the processing amount for decoding is larger, thedriving frequency may be set higher, and when the processing amount fordecoding is smaller, the driving frequency may be set lower as themethod for setting the driving frequency. Thus, the setting method isnot limited to the ones described above. For example, when theprocessing amount for decoding video data in conformity with MPEG-4 AVCis larger than the processing amount for decoding video data generatedby the moving picture coding method and the moving picture codingapparatus described in each of embodiments, the driving frequency isprobably set in reverse order to the setting described above.

Furthermore, the method for setting the driving frequency is not limitedto the method for setting the driving frequency lower. For example, whenthe identification information indicates that the video data isgenerated by the moving picture coding method and the moving picturecoding apparatus described in each of embodiments, the voltage to beapplied to the LSI ex500 or the apparatus including the LSI ex500 isprobably set higher. When the identification information indicates thatthe video data conforms to the conventional standard, such as MPEG-2,MPEG-4 AVC, and VC-1, the voltage to be applied to the LSI ex500 or theapparatus including the LSI ex500 is probably set lower. As anotherexample, when the identification information indicates that the videodata is generated by the moving picture coding method and the movingpicture coding apparatus described in each of embodiments, the drivingof the CPU ex502 does not probably have to be suspended. When theidentification information indicates that the video data conforms to theconventional standard, such as MPEG-2, MPEG-4 AVC, and VC-1, the drivingof the CPU ex502 is probably suspended at a given time because the CPUex502 has extra processing capacity. Even when the identificationinformation indicates that the video data is generated by the movingpicture coding method and the moving picture coding apparatus describedin each of embodiments, in the case where the CPU ex502 has extraprocessing capacity, the driving of the CPU ex502 is probably suspendedat a given time. In such a case, the suspending time is probably setshorter than that in the case where when the identification informationindicates that the video data conforms to the conventional standard,such as MPEG-2, MPEG-4 AVC, and VC-1.

Accordingly, the power conservation effect can be improved by switchingbetween the driving frequencies in accordance with the standard to whichthe video data conforms. Furthermore, when the LSI ex500 or theapparatus including the LSI ex500 is driven using a battery, the batterylife can be extended with the power conservation effect.

Embodiment 12

There are cases where a plurality of video data that conforms todifferent standards, is provided to the devices and systems, such as atelevision and a cellular phone. In order to enable decoding theplurality of video data that conforms to the different standards, thesignal processing unit ex507 of the LSI ex500 needs to conform to thedifferent standards. However, the problems of increase in the scale ofthe circuit of the LSI ex500 and increase in the cost arise with theindividual use of the signal processing units ex507 that conform to therespective standards.

In order to solve the problem, what is conceived is a configuration inwhich the decoding processing unit for implementing the moving picturedecoding method described in each of embodiments and the decodingprocessing unit that conforms to the conventional standard, such asMPEG-2, MPEG-4 AVC, and VC-1 are partly shared. Ex900 in FIG. 42A showsan example of the configuration. For example, the moving picturedecoding method described in each of embodiments and the moving picturedecoding method that conforms to MPEG-4 AVC have, partly in common, thedetails of processing, such as entropy coding, inverse quantization,deblocking filtering, and motion compensated prediction. The details ofprocessing to be shared probably include use of a decoding processingunit ex902 that conforms to MPEG-4 AVC. In contrast, a dedicateddecoding processing unit ex901 is probably used for other processingunique to an aspect of the present disclosure. Since the aspect of thepresent disclosure is characterized by inverse quantization inparticular, for example, the dedicated decoding processing unit ex901 isused for inverse quantization. Otherwise, the decoding processing unitis probably shared for one of the entropy decoding, deblockingfiltering, and motion compensation, or all of the processing. Thedecoding processing unit for implementing the moving picture decodingmethod described in each of embodiments may be shared for the processingto be shared, and a dedicated decoding processing unit may be used forprocessing unique to that of MPEG-4 AVC.

Furthermore, ex1000 in FIG. 42B shows another example in that processingis partly shared. This example uses a configuration including adedicated decoding processing unit ex1001 that supports the processingunique to an aspect of the present disclosure, a dedicated decodingprocessing unit ex1002 that supports the processing unique to anotherconventional standard, and a decoding processing unit ex1003 thatsupports processing to be shared between the moving picture decodingmethod according to the aspect of the present disclosure and theconventional moving picture decoding method. Here, the dedicateddecoding processing units ex1001 and ex1002 are not necessarilyspecialized for the processing according to the aspect of the presentdisclosure and the processing of the conventional standard,respectively, and may be the ones capable of implementing generalprocessing. Furthermore, the configuration of the present embodiment canbe implemented by the LSI ex500.

As such, reducing the scale of the circuit of an LSI and reducing thecost are possible by sharing the decoding processing unit for theprocessing to be shared between the moving picture decoding methodaccording to the aspect of the present disclosure and the moving picturedecoding method in conformity with the conventional standard.

The herein disclosed subject matter is to be considered descriptive andillustrative only, and the appended Claims are of a scope intended tocover and encompass not only the particular embodiment(s) disclosed, butalso equivalent structures, methods, and/or uses.

INDUSTRIAL APPLICABILITY

The picture coding method and picture decoding method according to oneor more exemplary embodiments disclosed herein are advantageouslyapplicable to a method of coding moving pictures and a method ofdecoding moving pictures.

The invention claimed is:
 1. A picture coding method for coding apicture, on a block-by-block basis, to generate a bitstream, the methodcomprising: performing a third derivation process for deriving thirdmerging candidates, each of the third merging candidates including acandidate set of a third prediction direction number, a third motionvector, and a third reference picture index for use in coding of acurrent block, the third motion vector and the third reference pictureindex being used for coding another block, the other block being decodedbefore the current block is coded, and the other block being differentfrom the current block; performing a first derivation process forderiving a first merging candidate which includes a candidate set of afirst prediction direction number which indicates bi-predication, afirst motion vector, a first reference picture index, a fourth motionvector, and a fourth reference picture index for use in the coding ofthe current block, the first motion vector and the first referencepicture index being included in one of the third merging candidates, thefourth motion vector and the fourth reference picture index beingincluded in another one of the third merging candidates; performing asecond derivation process for deriving a second merging candidate whichincludes a candidate set of a second prediction direction number, asecond motion vector, and a second reference picture index for use inthe coding of the current block, the second motion vector being a zeromotion vector; selecting a merging candidate to be used in the coding ofthe current block from among the first merging candidate, the secondmerging candidate, and the third merging candidates; and attaching anindex for identifying the selected merging candidate to the bitstream,wherein in the performing of a first derivation process, the firstderivation process is performed so that a total number of the firstmerging candidates does not exceed a first predetermined number, thesecond derivation process is performed when a total number of the firstto third merging candidates is less than a second predetermined number,the second predetermined number being a maximum number of the mergingcandidates, and the second predetermined number is different from thefirst predetermined number when the second derivation process isperformed.
 2. The picture coding method according to claim 1, whereinthe first predetermined number depends on a maximum number of the firstmerging candidates to be derived using the first derivation process. 3.The picture coding method according to claim 1, further comprisingswitching a coding process between a first coding process conforming toa first standard and a second coding process conforming to a secondstandard, according to identification information attached to thebitstream and indicating either the first standard or the secondstandard; and attaching, to the bitstream, identification informationindicating either the first standard or the second standard to which thecoding process after the switching conforms, wherein when the codingprocess after the switching is the first coding process, the firstcoding process is performed by performing the first derivation process,the second derivation process, the selecting, and attaching.
 4. Apicture coding apparatus which codes a picture, on a block-by-blockbasis, to generate a bitstream, the apparatus comprising: a processor;and a non-transitory memory having stored thereon executableinstructions, which when executed by the processor, cause the processorto perform: performing a third derivation process for deriving thirdmerging candidates, each of the third merging candidates including acandidate set of a third prediction direction number, a third motionvector, and a third reference picture index for use in coding of acurrent block, the third motion vector and the third reference pictureindex being used for coding another block, the other block being codedbefore the current block is coded, and the other block being differentfrom the current block; a first derivation process for deriving a firstmerging candidate which includes a candidate set of a first predictiondirection number which indicates a bi-prediction, a first motion vector,a first reference picture index, a fourth motion vector, and a fourthreference picture index for use in the coding of the current block, thefirst motion vector and the first reference picture index being includedin one of the third merging candidates, the fourth motion vector and thefourth reference picture index being included in another one of thethird merging candidates; performing a second derivation process forderiving a second merging candidate which includes a candidate set of asecond prediction direction number, a second motion vector, and a secondreference picture index for use in the coding of the current block, thesecond motion vector being a zero motion vector; selecting a mergingcandidate to be used in the coding of the current block from among thefirst merging candidate, the second merging candidate, and the thirdmerging candidates; and attaching an index for identifying the selectedmerging candidate to the bitstream, wherein the first derivation processis performed so that a total number of the first merging candidates doesnot exceed a first predetermined number, the second derivation processis performed when a total number of the first to third mergingcandidates is less than a second predetermined number, the secondpredetermined number being a maximum number of the merging candidates,and the second predetermined number is different from the firstpredetermined number when the second derivation process is performed. 5.The picture coding method according to claim 1, wherein the other blockis adjacent to the current block in the picture.
 6. The picture codingmethod according to claim 1, wherein the first predetermined number isless than the second predetermined number.